I'm really surprised no one asked this yet.. I've been trying to find this for a while now, but I've taken matters into my own hands..
I've been trying to find the DBC for changing NPC clothing.. I thought it might have been "CreatureDisplayInfoExtra", I tried to fetch the itemID's in the "m_NPCItemDisplay" columns... and it didn't seem to match the NPC's that I've chosen. If anyone could lead me in the right direction.. that would be great! Thanks.
EDIT: Using Orc Model, Creature