Dunno about defacing people's xmas decorations, but how about adding stuff, maybe Easter bunnies (it's just around the corner!), Cinco de Mayo, and 4th of July (why are you taking that down - do you hate America?!?)
This could actually be a yearlong PatNet project. After every theme holiday, from Valentine's to Secretary's Day, we could ask local retailers for their leftover displays that they're throwing away. Then, when the early Christmas displays show up in the store windows, add everything back. It's an omni-holiday celebration!