The biggest problem I've found with freezing royal iced cookies is that the colors will often bleed
once the cookie thaws. If your snowflakes are all in white, you shouldn't have a problem. If they're multicolored, you might have a little trouble - just be sure to let them sit undisturbed until they are completely thawed and free from condensation.
I bake and decorate cookies as a side business, and I agree with Marilyn that you can usually decorate ahead - seal the cookies in bags once they're dry, and you'll be fine for a couple of weeks (depending on your recipe, of course - a typical sugar or spice cookie will be just fine).