mess up your crank? The worst I can see happening with a slip on type like that is it gets loose and it stops spinning the supercharger and the alternator and just spins free. You will notice that immediately with power loss but there wouldn't be any real damage. You could either keep a spare stock length belt in the trunk in case and pop it off on the side of the road and go stock in an emergency, or you could re-tighten the pulley.