Replaced the front tire on by 07's 600 and noticed that one of the rotors had some play on the circular rivets. Anyway to fix this or do you have to replace the rotors?

If these are OE rotors there is nothing that can be done. Some folks in the past have put a bit of silicone or some sort of glue ont he button area to prevent from constant movement but the reality is that the washers are worn down.
If this is an OE replacement rotor, you could contact whom ever made it and ask them if they offer a button replacement kit. One last thin, some play is not too bad as long as the friction blade does not move more than 1.2mm side to side.
Good luck, and keep an eye on them !

a little bit of play is fine, but if its anything significant (basically if you can shake it back and forth with your hand noticeably) you should replace it. Mine were like this at one point and got so bad that I was scared to ride it until the new ones came in. I just ordered a used one off of ebay and it has been fine for over a year now