I freeze iced cookies all the time.  I place them in large zip loc bags, and suck out as much air as possible before sealing and placing in the freezer.  When I need the cookies, I take the bag out but DON'T OPEN IT until they are thawed or at room temperature.  That way condensation forms outside the bag and not on the cookie, leaving the icing in pristine condition.  Works perfectly every time for me.