I decided to try modding this game again and sadly little came out of it. As for porting meshes from the new version into the old one, I found that once you do it, the new mesh will be invisible. This issue is apparently caused because of meshes that have physics tied to them, which will cause that unless the exact specific mesh is there, the model won't be visible, so unless I figure how to find these values and import them aswell, it won't work. I could do a test with meshes that don't move to see if that's the case, but I kinda give up on that.
At most, seems like texture editing is as far as modding for this game will go unless someone who really knows Unity and il2cpp gives it a shot. It sucks, but it's not so bad either since the clothing damage masks can be helpful. Since they hide parts of the mesh and texture to give the effect of thorn clothes, I figure they can be altered to get some variety. I was trying to make a custom mask to get a version of Lorena's outfit without the shirt underneath, the only problem is that I don't know why the mask I made didn't work and erased to whole outfit instead of the selected area. If anyone has a clue of why this happened, I'd really appreciate it. Maybe some good can still come out of this, just wish the dev had left some tool behind.
Some quick stuff I made editing textures with Photoshop. Second one doesn't look as good as it seems, sadly, but it's as good as I'll get until I figure how to use the masks, if that.