I haven't had many experiences as CO-GM, but every time I am, it's usually that you have to talk to the GM whenever you want to make changes.

Though, usually, CO-GMs can accept CSs at will, it should in theory still fall under main GM permission to pull characters. Requesting changes is fine, but pulling a sheet when it's already been accepted is too far, from my perspective.

Though, that's my opinion from my past experiences ^~^