That will only allow you to attack other players with the pvp flag on.
There is no command to actually take over and control an npc.  You need to make a new character, #name it what you want it called, #permarace it to the race you want, #level it, etc.  Turn your gm flag on (#gm on), then use /becomenpc <npcrace>
In my experience that tacks an annoying "Trader" title to your name, though.  So, you'll become "Trader Mummy Leader". If you don't like that, you can avoid using /becomenpc, and just make a #damage hotkey to use instead of attacks.  But, it wouldn't really be fair, because the players can't attack back.  They CAN attack you if you use the /becomenpc command.  In short, there's no good way to do what you're trying to do, but I'm with you 100% that we need a better solution.
				__________________
				The PEQ Database Editor is available!
Edit Loot, NPCs, Spawns, Merchants, Factions, NPC Spell Lists, and Tradeskills with ease!
Check it out!