Sim Enhancer requires your User Data to be in the same folder as the sims.exe and in the same folder as your data (skins, heads, that sort of thing)
Sims Legacy does not store your user data in the User Data files in the steam (or ea) folder, instead it stores your save data in the Users/Save Games/Electronic Arts folder by themselves, if you tell Sim Enhancer where your sims.exe file is it won't work because the save data in that folder is never used, and if you try to direct it to the Users file then it won't have access to any of your skins or heads. Hopefully soon a new application will come out to let you do this stuff, but currently it isn't possible.

Sim Enhancer is a VERY useful program, but a lot of what it does can be done by other mods. The supersculpture at Some Sim Things lets you alter interests and skills, C&C's dresser lets you change your sim's outfits, the personality bookcase at Some Sim Things lets you alter personality points, and so on. The supersculpture lets you maximize a skill with one click; if you want to add one point at a time, my Skill Picture will do that.

If you have a copy of The Sims 1 installed in the old place, it might be possible to copy the saved games into that installation as Neighborhood 9, alter them with the Enhancer, then transfer them back again. But most people who've bought Legacy probably don't also have the old Sims 1 also installed. :-)

Edited to add: I just tried the trick of moving from one installation to another and back again, and when I did, the EA App told me that some of my files were corrupted. I did make some fairly extensive changes, so it's possible that smaller changes might work. But at least for what I did, Legacy did not like the UserData file that was altered by Sim Enhancer.

I can confirm that altering a save from the Legacy Edition with SimEnhancer will corrupt the save beyond repair! Even if it's a save started with the Complete Colletion and then transfered to the Legacy Edition - once you save the game through the Legacy Edition, DO NOT edit it with SimEnhance as even the smallest change will render your save unplayable, and transferring it back to the Complete Collection won't recover it.
I guess this could only mean that the Legacy Edition does something different when it saves the game, compared to the Complete Collection.
The Sims 2 Legacy Edition has been notorious for corrupting saves on its own, and I believe the same thing could be happening with the Sims 1 Legacy since many player have reported multiple game crashes (which often times is a sign of save corruption).
I don't trust the Legacy Edition, it's not safe to play and save corruption is really a thing, which is why I'm sticking to the Complete Collection.

Only EA would manage such a thing. Sigh.

@carlao1124 What were the indications of corruption? I want to use the SimEnhancer to edit the interests of premade sims, I don't like how they're randomized so I'd prefer to take a more calculated approach pre-gameplay. From my brief testing, it seemed that making a backup of the UserData in the Steam Installation folder, then replacing this with a copy of whats in the Saved Games location that has already been saved once post-first launch, then using the SimEnhancer from the Steam Installation Directory to change interests and saving, then copying over just the specific character file (and perhaps the Neighborhood file too) into the Saved Games location then restoring the Steam files from the backup seems to work fine...but there's a lot more testing to be done and I'm worried I'll be in for a nasty surprise.

I lost an entire save because I started it with the Legacy Edition and then edited it with SimEnhancer. The game crashes right before the Neighborhood screen (and after the splash logo). Luckily, I could still load that save in SimEnhancer, so I literally copied every piece of information on my sims, and then re-created everything in a brand new save. I made another test where I started a new save with the Legacy Edition, then I edited only 1 sim with SimEnhancer and it corrupted that save too, so at least on my end (and as Corylea confirmed it too) , that's what's going on. It seems to break only your sims, but you can sill transfer your lots to a new save. I decided to settle for the Ultimate Collection, which has always worked great all these years. It's a shame because I really wanted to play the re-release, but I don't wanna risk losing a save and, like you, I need SimEnhancer to make the Townies the way I want them.

Thanks for clarifying! Sorry you lost a save. I thought I had it working with the Legacy Collection for a moment, until I tried to edit any of the premade Unleashed families like Goth Sr or Claire Charming, then my game would crash during launch. Luckily I'm just in a testing phase and have backups so would restore anything I experiment with anyway. It seems to be a problem with the way SimEnhancer saves data. I have also installed the Complete Collection and found that there's no problem in making the edits to that with SimEnhancer and then copying those saves from the Complete Collection to Legacy Collection, that works absolutely fine, the issue is with directly saving LC files with the SimEnhancer.

I just added SimExplorer and it is working with the new Legacy Sims.
I've uploaded it to my SimsFileShare if anyone needs it.
I am going to test more of the older programs to see if they are compatible with the Legacy Sims.
http://simfil.es/5335673/

I also added SimCatagorizer and it is working. You just need to set the path to where the game is loaded.
I'll share the program here too if anyone wants it.
http://simfil.es/5335674/

SimCatagorizer i keep getting error even with VB6 runtime...

That's because it needs Visual Basic 6 runtime installed in order to run. It's not a Legacy specific bug. The readme mentions this:

VB6 Runtime is Visual Basic 6 runtime, still keeping error as i check i did installed it, then i give up and use SE Object Manager it did work but still paid and i use free try.

May I ask whether Transmogrifier works with Legacy? I was reading Corylea's tutorial on hacking objects on Reddit, but it's pre-Legacy.

The Transmogrifier looks for The Sims, so it MIGHT not be able to find The Sims Legacy. I don't know if it searches registry entries, or if it searches files. I think it searches for sims.exe, though, and the Legacy game still has that.

IF it can't find your installation of The Sims, there are two possibilities:

If it searches files, then you could try making folders Maxis\The Sims in your Program Files (x86) directory, then copying all of the Legacy files to C:\Program Files (x86)\Maxis\The Sims. Objects cloned would be in C:\Program Files (x86)\Maxis\The Sims\Downloads\Transmogrified, but it would be a simple matter to move them back to your Legacy installation.

If it searches the registry, then getting it to work would require hacking the registry to add an entry for The Sims, then doing the file copying mentioned above. It's VERY easy for things to go wrong when hacking the registry, so I really don't recommend it, but it is a way...

But I THINK it looks for sims.exe, and if it does, it should work with Legacy. (I can't test this for you, because I also have The Complete Collection installed, and have had TMog working with TCC for several years now.)

By default, I think T-mog looks for your install path using the registry... but it ALSO includes in its "About the Sims Transmogrifier..." button an option to set the Sims install path, where you can tell it where your Sims exe is! (I opened T-mog just to confirm this because there are SOME programs that guess via the registry but let you manually set the location if the registry entry is wrong or missing for whatever reason.)