For a mod I'm making, I want to base one of my NPC's off someone I know IRL. Is there a utility that allows me to transform a picture of a person's face onto an in-game NPC?

no utility, but there is a method to do this in a tutorial by lochnarus http://www.mwmythicmods.com/tutorials/loch_face_texturing.htm

ST
ps, works easy enough in GIMP as well