When you throw a costume party, guests change into random costume outfits selected from a pre-made outfit list. I’ll show how you can add your own outfits to this list.

Required Programs:

• S3PE
• SimOutfitter
• S3OC (Optional)
• CTU (Optional)

Pro Steps:
1) Copy the “TrickOrTreatSituation_0x89121649c768f2d7” XML file into a package. It’s inside the GameplayData.package in the base game folder.
2) Make up unique names for your outfits, add them to the appropriate lists inside the XML file.
3) Create your outfit files using the SimOutfitter tool. Use the unique names you made up before so that you get the correct instance IDs.
4) Import your outfit files into your package. Change their group numbers to “0x78000000”.
5) Save. Load. Done.

Beginner Friendly Steps:
1) Creating tuning package

• Open S3PE. Go to File>Open. Navigate to “*wherever your game is installed*\Electronic Arts\The Sims 3\Game\Bin\Gameplay”. Select “GameplayData.package”. Tick “Open as read-only” so that you don’t make changes accidentally. Click Open.
• At the bottom, there are fields for filtering. Paste “0x89121649C768F2D7” into the Instance field. Tick the box next to Instance field. Click “Set”. Tick the “Filter active” box. Now you should only see the “_XML” resource named “TrickOrTreatSituation_0x89121649c768f2d7”. This is the tuning file we will be overriding. Select that, right-click on it, Export>To package. Give a name to it, let’s call it “MyCostumePartyOutfitMod” for this tutorial. It will save the new package when you click Open.
• We’re done with GameplayData.package, close it.

2) Editing the XML tuning file

• Open your MyCostumePartyOutfitMod.package with S3PE. Right-click the _XML resource, click “Text editor”.
• You will find the lists we want to edit at the bottom of the text file. They are named kChildCostumeNames, kTeenMaleCostumeNames etc. Names are self-explanatory. -(Elders use the adult costumes.)
• Now think of unique names for your outfits. Later, this will help us get unique instance IDs for our outfit files so that they don’t conflict with others. EA’s outfit names go like tmBodyEP8Costume5, afBodyEP8Costume12 etc. Similarly, we can name our outfits in a format like “age-gender-costume-username-number”. That should be unique enough. I will create an adult female outfit for this tutorial and name it “afCostumeSlamyy01”.
• Now add your outfit names in the appropriate lists. I added mine at the beginning of the list; you can add wherever you like but make sure you add the comma and space properly. Add as many as you like, each having a unique name. You can also remove EA’s outfits from the lists.
• Save the text file. When you close the text editor, S3PE will ask if you want to commit the changes, say Yes. Save your package.

3) Gathering clothing packages
We want to add clothing parts to our outfit like shoes, top, hair etc. If you want a custom clothing piece, just copy the CC package file. If you want to use an EA clothing do this:

• Open S3OC. At the top, go to Cloning>CAS Part.
• Now find and select the clothing item you want from the list. The list is huge but you can click on the column labels at the top to sort by name and expansions to make it easier to find stuff. -(Also, if you use MasterController, while creating a sim, you can right-click on a clothing thumbnail, which shows its info and exports it into a file so that you can find it easier in S3OC.)
• At the right bottom corner, click “Clone or Fix”. The options show up. Untick “Deep clone”. Definitely untick “Renumber/rename internally”!!! You can enable compression and include thumbnails, doesn’t matter. Click Start. Save the package, name doesn’t matter.
• After you clone all the stuff you like, close S3OC, we’re done here.

4) Editing the design presets
To change the colors/patterns of a clothing part, we will use CTU. If you’re using a CC clothing, make sure to edit the copy, not the original.

• Open CTU. File>Open, select one of the clothing packages you gathered in Step 3.
• Go to “Designs” tab. Select one of the numbered designs. Under that, select the “Patterns” tab. Again, under that, there is “Patterns:” with the options “Pattern A,B,C,D”. Those represent the 4 main coloring channels you see in Create a Style in game. Not all 4 of them are available for every clothing. Select and edit each.
• If you want plain color, select “Solid Color” from "Type".
• If you want to use a pattern, click “Browse Patterns” button. If you chose a multi-color pattern, select “Pattern (Coloured)” from “Type”. "Pattern (HSV)" is for single color patterns.
• To change colors, at the bottom, there are color boxes, click on them to open the Color Picker window.
• When you’re done editing, go to File>Save. We’re done with CTU.

5) Exporting CASP files
Now we need to export the CASP files from the clothing packages.

• Open a clothing package with S3PE. Select the resource with the “CASP” tag. Right-click, Export>To file. Save without changing its name! Repeat for all clothing you gathered. -(Alternatively, you can merge all of them, then select and export all the CASP resources at once.)
• They are exported with “.caspart” extension.
• Now that we took the organs CAS parts of the clothing packages, they are useless, you can get rid of the packages if you like.

6) Creating the outfit files

• Open SimOutfitter. Go to File>New outfit (or “Open outfit file” if you want to edit an existing one).
• Important: In the outfit name field, you should paste your unique outfit name exactly as the way you wrote in the XML file in Step 2. This gives the outfit file an instance ID based on that name and that’s how the game will recognize your outfit. Mine was “afCostumeSlamyy01”.
• Make the appropriate age and gender selections.
• At the top, go to “Add CAS parts>Add from CASP file”. Open a caspart file that you exported in Step 5. If it has multiple design presets, it will ask you to pick one. Repeat and add all the clothing parts you want like this. For this tutorial, I added a CC flame dress by BEO and EA’s firefighter boots to my outfit. You can add other stuff like hair, makeup, accessories too.
• Go to File>Write outfit file. Save without changing its name!
• Repeat this step for all the outfits you want to create.

7) Importing the outfit files

• Open your MyCostumePartyOutfitMod.package in S3PE.
• Go to Resource>Import>From file. Select the outfit files that you created in Step 6. Don’t change anything in the Resource window, click OK. Your imported outfits are tagged “SIMO”.
• Double-click on your SIMO resources to open Resource Details. Change the “Group” number to “0x78000000”. Do this for all of them, otherwise they won’t work.
• Save your package. It’s ready.

8) Finishing
It’s over! Put your MyCostumePartyOutfitMod.package in your Mods folder. Make sure the originals of custom clothing you used are also in your Mods folder. Don’t put the EA clothing you cloned in your Mods. Clear your cache. Test in game
-(Also, I suggest removing most of the EA outfits from the XML file during testing. Otherwise, if you created only one outfit to just test, it will have a very low chance to get randomly selected among all the others and you will be throwing your 37th party trying to just roll that one outfit at 5 am sleepless like me. )


Bonus - Editing Existing EA outfits:

• In the TrickOrTreatSituation XML file, select and copy the name of the outfit you want. I copied "amBodyEP8Costume11".
• Open S3PE, go to Tools>FNV Hash. Paste it in the "Text to hash" field. Click Calculate.
• Copy the result in the "FNV64" field. I got "0xCBD2C70B1A053D2C". Close.
• File>Open, navigate to “*wherever your game is installed*\Electronic Arts\The Sims 3 Seasons\GameData\Shared\Packages”. Select "FullBuild_p16.package". Tick “Open as read-only”. Open.
• At the bottom, paste the FNV64 value that you copied before into the Instance field. Tick the box next to Instance field. Click “Set”. Tick the “Filter active” box.
• Now you see only one SIMO resource. That's the outfit you want. Right-click, Export>To file. Save without changing its name! Close S3PE.
• Open the outfit file in SimOutfitter and edit as you like. Don't write anything in the "Outfit name" field. Export(File>Write outfit file), save without changing its name!
• Open S3PE. File>New. Then go to Resource>Import>From file. In the resource window, don't change anything but you can write the name of the outfit so you will know what it is, just don't click any buttons next to it. Click OK.
• That's it, save the package and put it in your mods folder. This will override the original EA outfit.

Contents of EA's costume outfits
I also opened each of EA's costume outfits with SimOutfitter and noted down their contents. Should be useful knowing which is which when removing/editing.

Code:

afBodyEP8Costume1 0x30FF320AD3A56B0A mermaid
afBodyEP8Costume2 0x30FF320AD3A56B09 cheerleader
afBodyEP8Costume3 0x30FF320AD3A56B08 doctor
afBodyEP8Costume4 0x30FF320AD3A56B0F maid
afBodyEP8Costume5 0x30FF320AD3A56B0E chef
afBodyEP8Costume6 0x30FF320AD3A56B0D hotdog 1
afBodyEP8Costume7 0x30FF320AD3A56B0C ninja
afBodyEP8Costume8 0x30FF320AD3A56B03 soldier
afBodyEP8Costume9 0x30FF320AD3A56B02 astronaut
afBodyEP8Costume10 0xE70D1265A214E1CE rocker skull face
afBodyEP8Costume11 0xE70D1265A214E1CF firefighter
afBodyEP8Costume12 0xE70D1265A214E1CC flight suit
afBodyEP8Costume13 0xE70D1265A214E1CD burglar
afBodyEP8Costume14 0xE70D1265A214E1CA hockey mask
afBodyEP8Costume15 0xE70D1265A214E1CB tuxedo top hat
afBodyEP8Costume16 0xE70D1265A214E1C8 police
afBodyEP8Costume17 0xE70D1265A214E1C9 princess
afBodyEP8Costume18 0xE70D1265A214E1C6 bunny
afBodyEP8Costume19 0xE70D1265A214E1C7 cat 1
afBodyEP8Costume20 0xE70D1165A214E07B cat 2
afBodyEP8Costume21 0xE70D1165A214E07A hotdog 2
afBodyEP8Costume22 0xE70D1165A214E079 hotdog 3
afBodyEP8Costume23 0xE70D1165A214E078 snorkel
~~~
amBodyEP8Costume1 0x1772832519F43DEF hotdog 1
amBodyEP8Costume2 0x1772832519F43DEC cowplant
amBodyEP8Costume3 0x1772832519F43DED firefighter
amBodyEP8Costume4 0x1772832519F43DEA soldier
amBodyEP8Costume5 0x1772832519F43DEB police
amBodyEP8Costume6 0x1772832519F43DE8 scrubs
amBodyEP8Costume7 0x1772832519F43DE9 astronaut
amBodyEP8Costume8 0x1772832519F43DE6 ninja
amBodyEP8Costume9 0x1772832519F43DE7 paramedic
amBodyEP8Costume10 0xCBD2C70B1A053D2D doctor
amBodyEP8Costume11 0xCBD2C70B1A053D2C chef
amBodyEP8Costume12 0xCBD2C70B1A053D2F rocker mohawk
amBodyEP8Costume13 0xCBD2C70B1A053D2E cat 1
amBodyEP8Costume14 0xCBD2C70B1A053D29 cat 2
amBodyEP8Costume15 0xCBD2C70B1A053D28 burglar
amBodyEP8Costume16 0xCBD2C70B1A053D2B tuxedo top hat
amBodyEP8Costume17 0xCBD2C70B1A053D2A clown
amBodyEP8Costume18 0xCBD2C70B1A053D25 inspector
amBodyEP8Costume19 0xCBD2C70B1A053D24 flight suit
amBodyEP8Costume20 0xCBD2C40B1A053834 hockey mask
amBodyEP8Costume21 0xCBD2C40B1A053835 hotdog 2
amBodyEP8Costume22 0xCBD2C40B1A053836 hotdog 3
amBodyEP8Costume23 0xCBD2C40B1A053837 hotdog 4
amBodyEP8Costume24 0xCBD2C40B1A053830 snorkel
~~~
tfBodyEP8Costume1 0xD7E6E9D69E044E2F mermaid
tfBodyEP8Costume2 0xD7E6E9D69E044E2C hotdog
tfBodyEP8Costume3 0xD7E6E9D69E044E2D cheerleader
tfBodyEP8Costume4 0xD7E6E9D69E044E2A burglar
tfBodyEP8Costume5 0xD7E6E9D69E044E2B cat
tfBodyEP8Costume6 0xD7E6E9D69E044E28 bunny
tfBodyEP8Costume7 0xD7E6E9D69E044E29 alien
tfBodyEP8Costume8 0xD7E6E9D69E044E26 hockey mask
tfBodyEP8Costume9 0xD7E6E9D69E044E27 snorkel
tfBodyEP8Costume10 0xE1AD86AE8150D9ED long dress
tfBodyEP8Costume11 0xE1AD86AE8150D9EC cowboy
~~~
tmBodyEP8Costume1 0x50AD6F25BBAEE64A hotdog
tmBodyEP8Costume2 0x50AD6F25BBAEE649 cowplant 1
tmBodyEP8Costume3 0x50AD6F25BBAEE648 mohawk goth
tmBodyEP8Costume4 0x50AD6F25BBAEE64F skull face
tmBodyEP8Costume5 0x50AD6F25BBAEE64E cowplant 2
tmBodyEP8Costume6 0x50AD6F25BBAEE64D alien
tmBodyEP8Costume7 0x50AD6F25BBAEE64C burglar
tmBodyEP8Costume8 0x50AD6F25BBAEE643 cowboy
tmBodyEP8Costume9 0x50AD6F25BBAEE642 snorkel
tmBodyEP8Costume10 0xC59A271DEA314F8E hockey mask
tmBodyEP8Costume11 0xC59A271DEA314F8F clown
~~~
cuBodyEP8Costume1 0xC798B70B0B263069 alien (male)
cuBodyEP8Costume2 0xC798B70B0B26306A superhero (male)
cuBodyEP8Costume3 0xC798B70B0B26306B superhero (fem) 1
cuBodyEP8Costume4 0xC798B70B0B26306C superhero (fem) 2
cuBodyEP8Costume5 0xC798B70B0B26306D superhero (fem) 3
cuBodyEP8Costume6 0xC798B70B0B26306E superhero (fem) 4
cuBodyEP8Costume7 0xC798B70B0B26306F superhero masked (male)
cuBodyEP8Costume8 0xC798B70B0B263060 cowplant (fem)
cuBodyEP8Costume9 0xC798B70B0B263061 gnome (fem)
cuBodyEP8Costume10 0x4EAF70C3F1E4425B roman soldier (male)
cuBodyEP8Costume11 0x4EAF70C3F1E4425A hotdog (male)
cuBodyEP8Costume12 0x4EAF70C3F1E44259 pirate skull (male)
cuBodyEP8Costume13 0x4EAF70C3F1E44258 alien head only (male)
cuBodyEP8Costume14 0x4EAF70C3F1E4425F cowplant (male)
cuBodyEP8Costume15 0x4EAF70C3F1E4425E alien (male) 2
cuBodyEP8Costume16 0x4EAF70C3F1E4425D burglar (fem)
cuBodyEP8Costume17 0x4EAF70C3F1E4425C cat (fem)
cuBodyEP8Costume18 0x4EAF70C3F1E44253 bunny (fem)
cuBodyEP8Costume19 0x4EAF70C3F1E44252 clown (male)
cuBodyEP8Costume20 0x4EAF71C3F1E4442E snorkel (fem)

Well, hey, this thread is less than a year old, so it won't mind a bit of necro.

I'm poking around at creating costumes for the CAS parts in the Movie Stuff pack. I have two questions:

1. TrickOrTreatSituation does not appear to have any costumes listed for elders. It has unisex child and male/female teen and ya/adult, but no elder. I assume elders can change into costumes? I was never paying attention when I threw costume parties, but I don't recall elders not costumes. Does anyone have insight into this?

ETA: Oh, I just found the fine print that says elders use adult costumes....


2. Does anyone know of a good way to test a costume outfit once you've created it? Even if I throw a costume party, I'm not guaranteed that the costume will be chosen randomly.

For the latter question, what specifically are you asking? Are you asking to see how the outfit looks in game or are you asking to check if the outfit is properly registered?
For the former, the late CmarNYC's Sim Outfit Changing Script can allow you to enter in the TGI of the SIMO resource as seen in S3PE to apply the outfit on a Sim.
For the latter, I don't know if costume parties allow for selecting specific outfits to change into (it seems there is code for that for trick-or-treating), but one could write a script mod that logs the outfits and forcibly cycles through the outfits for each Sim (I might be able to do it later after work).
If neither are these are what you're asking, I apologize for not understanding.

You can remove existing EA outfits from the XML tuning for testing so that they can only pick your custom outfit.
Or if you just want to see the outfit in game, what Destrospean suggested sounds good.

Both of these suggestions are very helpful. Thanks!

You may be fine, but this script mod might make it easier for you to cycle through outfits without having to set up costume parties. You can also use this if you don't want to have to take out costume names to narrow things down.

There is one caveat, though, that being you have to switch to another outfit before switching into another random costume.

It seems like this will be a lot of help along with removing the other costumes from the adult list. Teens (and I presume children) have an interaction to choose a specific costume, but adults do not. That makes me want to create one. It's pretty annoying that the code is right there but is restricted to teens and children. But that's a task for another day.

The teen costumes I tried worked, though, so the system is sound!