After looking through some of the source code (utils/perlxs/npc.h & utilz/perlxs/mob.h), there are a few commands that
might accomplish what you're looking for using a quest script, but I'm not really sure because the syntax of the commands aren't very clear:
Code:
SetAppearance(EmuAppearance app, bool iIgnoreSelf = true);
EmuAppearance GetAppearance();
If that doesn't provide the functionality, it sounds doable, but code would have to be created to manipulate the Spawn_Struct for the NPC, I believe.