Well, I just did it and it worked fine. You don't have to return the plates, you just have to say you're holding on to them and they put that in their system.
1998 BMW 328is - summer
1993 BMW 525i - daily
1994 BMW 325i - sold
1992 BMW 325i - gone
1988 Mercedes Benz 190E 2.3-8V - sold