>how do you transfer back to a broker

Lol

> sell a few

Excuse me? We don't do that here.

> but when you need to sell some shares for funds

If you don't want true ownership, then that's your own fault when you get nothing at the end ;). You can sell directly out of CS without issue (as they have their own broker that they use), but TBCH, I'm fairly certain you already knew that.