Is it possible...

[Athrin Onu]

...to remove all the NPCs from an instance? Let's say. I dunno, there's that nice chest in Stratholme that I like looting. Why not remove all the NPCs from that dungeon and keep running it over and over again, looting the chest a bunch.

[A_Snake01]

Nope. NPC spawns are server side.

[Athrin Onu]

Nope. NPC spawns are server side.

Well, how about moving where they spawn to a different location?

[A_Snake01]

NPC Spawns are serverside. Must I knock sense into you?

You cannot control where an NPC spawns. You cannot control an NPC loot table. You cannot control an NPC anything. Chests work this way too, they count as NPCs. There is nothing you can do about it.