Is it possible to give a CAS part a second texture "overlay"?
To clarify, I mean having one object in CAS (let's say, a hat for example) apply its texture with a higher composition method, as if it were taking over some of the duties better reserved for makeup or skin details, while simultaneously applying a texture over-top (or, ideally, underneath) that with a composition method of 0, to prevent the issue of a composition method 4 hat's actual geometry showing a pure black texture in-game.
To put it another way, can you do anything similar to adding overlays to skin colours, but do it for CAS parts which are not skin colours?
Alternatively, (and sorry, this isn't really CAS-specific but I didn't want to make two topics asking for two solutions to the same problem) is it possible to edit .GEOM data in plain text, the way it's displayed in Sims 4 PE? I have no idea if it would actually work but if I could adjust the UV stitch data (find and replace "]: X: 0.5" with "]: X: 0.0" would do it) I could move the textures onto the scalp/hair area. It might get ruined as soon as you add hair (I have no idea how the textures would interact, to be honest) but it also might just give the hat parts just the skin data they need to properly composite their texture on top of.
I'm completely aware I'm performing some dark magic the game is not meant to have to deal with, but if I can get all of these disparate parts working properly together I will be VERY happy with the end result.
I found where you can edit GEOMs once I knew it existed, and yeah, that's not happening for these meshes. I wanted to move them, because the model part used texture-space in the hats section of the diffuse map, but to get the body part of the texture to mix well I needed to use composition method 4; basically the skin looks fine this way, but the hat part was pure black.
That's fine, though. I had a couple things I wanted to do, but moved the goalposts to be much more ambitious once I found out how easy it all was. I could probably force the overlay using a script mod, but that'd be crazy AND inefficient, compared to just... using two different things in CAS.