Hi!I'll be very grateful if we were still able to change our username before a multiplayer game actually started. I've become fed up of the Forum name that I can't change, but that's fine because it's only on the forums. However, I never ever use it for playing MP games and I don't want to be forced to do so.
You should still be able to do that in the lobby. It will default to your username though. The feature of changing your in-game nickname per game has not been removed. Please let me know if you don't get it to work!