The effects allowed by that rule are ones that work on just the 64x64 area. What you want sounds similar to the web allowance for borders:
My game is for web, can I add border art outside the 64x64 limit? YES! As long as it's part of the page and not rendered by the game.
The difference is yours would be rendered by the game/Unity. If you really want to do it, go ahead, but my advice would be to have it as an option which is off by default. As I usually say for these questions, you will not get disqualified for doing it but the people rating your game might be a lot stricter!