I've been looking for this information through Apple documents, but could not find the answer. Soon after I launch my Game Center app there is a pop-up that says:
Welcome back, PlayerName
How can I hide the "Welcome back, playerName" message from Game Center when the player authenticates?
No, there's not. You can't change the behavior of iOS services (which GameCenter is part of) without jailbreaking the device and rewiring them. And out of curiosity - why do you need that?