LINE large baking sheet with sides with wax paper. With a small metal spatula or butter knife, spread a thin layer of frosting on each cone (Be sure to save some frosting to adhere cones to cookie hat base! About 3/4 cup will be needed.) Place frosted cones on baking sheet. Sprinkle with sugars and sprinkles. Let stand for 1 hour to allow frosting to set.
MEANWHILE, PREPARE cookies as directed on package. Cool completely.
FILL plastic bag with remaining icing; seal. Cut 1/4-inch corner from bag. Squeeze bag to pipe icing around bottom of each cone; adhere cones to each cookie to form hats. To decorate base of hat, use different colors of decorator icings and sprinkle with additional sugars or sprinkles.