Well, it's not a perfect solution... I took my standard light set and "turned off" all the lights by clicking off the "On" buttons in properties. I then saved this as a light set. When I want to change light sets, I click on the "Lights Off" set first, then click on the new light set. This turns all the lights off but doesn't remove them. It tends to work even when I have more lights on than I have off (if that makes any sense whatsoever). It's imperfect, but it's alot faster than selecting and deleting 20 lights at a time.