Two days in advance: Make royal icing snowflakes. Tape pattern to board; cover with waxed paper. Spray lightly with pan spray; wipe off excess. Pipe snowflake with tip 2 lines and dots, using royal icing and heavy pressure. Let dry overnight. Gently slide piece of paper under snowflakes to loosen. Carefully turn over snowflake and overpipe with tip 2. Let dry overnight.
Ice cupcakes smooth in buttercream. With knife, cut a small hole in cupcake top; insert snowflake. Position cupcakes on pedestals.