Hello, I believe you're referring to one of my posts. To answer you and LeBurns questions:
- Yes its definitely possible to port NPC hair to the PCs. There is a catch though: you have to overwrite an existing PC hairstyle to add an NPC one.
I've been wanting to write a tutorial on creating a basic model/texture swap mod and using a hair swap as an example seems like an ideal template. Just not looking forward to it because I don't really like writing tutorials and suck at explaining things :P
- Replacing PC heads with NPC heads is a messier process. There is technically only one PC head model for each gender. On the other hand each NPC head has its model and, the real issue, their own unique texture layout. Thus simply trying to paste an NPC head texture over a PC one will just make your player look like surrealistic nightmare

And if you replace a PC head model with one of the NPC ones you'd have to replace ALL the face textures of that gender with ones formatted to the texture layout of the NPC head model you used. So yeah, pain in the butt.
- I haven't tested trying to replace the male player body with Jahan's smaller one, but I've been meaning too. Should be an easy test, since Jahan's body appears to be handled by only one model. So swapping the player body with it should be a quick and easy process. Which will either work or completely fail suggesting Jahan's body scaling is handled by some LSB/LSX file buried in the mess of them. Just hopefully not a hard coded feature....
EDIT: Bah, it appears Jahan's body scaling is handled somewhere in the coding, not by a mere model swap

I guess I can trying digging around to see if I can find it, but making no promises. Annoying....