Jumping out after the goal has been reached makes no sense to me.
If you decide to commit to something, then commit. Don't puss out in the end.
I agree. If you're not sure, don't back at all. If you changed because of changes to the reward system after you pledged, well, ok, but that's a bit weak. If you changed because of changes to the project itself after you pledged, fine, but then I would say next time wait till the end to pledge. There's no bonus points for pledging early unless you're going for an expensive limited slot you're worried will be filled up.
The Jedi Master