Solving the problem

Okay, lesson learnt here, and I want everyone reading this to acknowledge this too :

DO NOT SKIN A CHARACTER PRIOR TO LAYING OUT ITS UVS!

It is messy. I think that duplicating the mesh, deleting its history, laying out its UV's and then transferring the UV's from the duplicate head to the main head might work. But it's messy, and there's no way to delete that transfer attributes history node. So your textures will always be getting reference off the other head. I'll test it now, maybe it'll be sufficient for this project.