I have read on quite a few cupcakery sites where they tell you to freeze the cupcakes, frosting and all. I'm pretty sure it won't hurt the cake nor the frosting. You can freeze frosting and use it later too, so whether it is on top of a cupcake should not make a difference.
What I would do is freeze them a little bit first and then cover them tightly and then stick back in the freezer. I am thinking that this way the frosting won't get snooshed and it will look just as good when you thaw them.