technically easy is just moving/scaling.. texture coordinates. But they will be applied to all vertices. Ie the whole head uv layout is moved around in the texture. Just doing for "some" would be more messy. what I would do is create a uv-layout with only the customizations (like the topleft image) and generate this…
It would require some coding and maybe an custom export plug-in to work in whatever engine. BUT you can assign it different Map Channels for each customization. I'm going to assume you are using Max? 1) First save your UV layout, because when you change the map channel it resets the UV's. 2) Add a new UnwrapUVW modifier.…