The Quarm event is already setup in PEQ. I know because I wrote it. NPCs 223991-223994 in potimeb.
You do not want to change the texture of a single NPC, you want to use 4 different NPCs each with a different texture. This is how it works on Live, because each time a head is killed, Quarm is stripped of all buffs and debuffs and you have to re-target him.
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