Half your ideas are libel to get you into some kind of trouble when you eventually get caught. Very few high schools will just overlook a prank that ruins their property in some way, shape, or form.

The best prank I ever heard about was actually an anti-prank. A group of seniors showed up with lawnmowers and cleaned up the entire school.

My high school banned senior pranks and threatened to press charges and expell anyone who took part in one.