Sometimes I want to move items lower, such as non-shiftable wall items that I think sits too high. I can use OMSPs or OmedaPixel's decorating tools mod to achieve this, but lowering the item technically pushes its footprint into the room below. Thus, it will also be visible when viewing the lower floor, and if I turn on object hiding, the object will disappear from the upper floor. (And of course this also causes its lighting to be based on the lower floor instead of the room it's intended to be part of.)

I searched around for a different type of OMSP that might avert this but don't see anything that looks like it would behave any differently from the ones I have now. Is there some other sort of finagling I can do that would solve this? One of the objects I'm trying to do this with is a sims3pack so I can't edit it in S3PE to add shiftability (if that would even work).

My guess is the answer to all this is probably no, but I figured it couldn't hurt to ask. Thanks!

Sims3packs can be (and generally should be) converted to .package with Delphy's Multi-Installer.
Most wall decor can indeed be made shiftable, there are many default replacements on this site for most EA cabinets, mirrors, etc.

For non-wall decor, you'd probably need to edit the mesh itself to place it lower.

If my DCBackup folder is to be believed, I have over 2,000 sims3packs installed, so it's a little late for that... 😳