Character head question

[beedeetwelve]

Hi y'all,
just wondering - do NPC's all share the same character head model? I wanna turn Teimo into Barbo, as seen here -EDIT- crap, it's a long video, I specifically mean at 38m00s :

but digging around in the game files, I haven't had a lot of luck figuring out where the head models are at, or how many there are.
Thanks for your time!