I know what you're talking about like when you change from a non to a mem and then you're level triples or something.
I personally haven't gotten the rookie medal even after the change, but I've gotten the MVP medal as a mem. I guess you just have to play a lot of fashion shows, give lots of stickers, lots of missions, (thats a lot of work T__T) but I guess its worth it?
My friend has been a rookie two times.. that's what they said that they did lol xD