Tint canned creamy white frosting with red paste or gel food coloring, leaving some white for the hat rims.
Place red-tinted frosting in a pastry bag fitted with a large round tip. (If frosting is too soft to hold its shape, chill for 30 minutes at a time until firm enough to work with.) On the cupcake, pipe frosting in a spiral that gets smaller as it nears the top. Top the hat with a mini marshmallow.
Place remaining white frosting in a pastry bag fitted with a small to medium star tip. Pipe small stars around the rim of the cupcake to create the hat rim.