From The TimeSplitters Wiki

Monkey Assistant Glitch
Requirements	TS2
Finder	Slagar

Create a map in Mapmaker, then set the recommended bot set so that all the bots are Monkeys. When the map is played, the player(s) will be alone with the bots spawning as if they were all Monkey Assistants. However, if you try to play monkey assistant in a premade made (Chinese, for example), it will either not allow monkeys or turn all the monkeys into Jungle Queen.

This is only possible in mapmaker maps.