The head won't warp if you remove that one bolt and reinstall it. If you remove the head, you'll need a new head gasket. If it's not seeping around the gasket, it's likely that doing one bolt will be OK.
FYI, the shop manual calls for removing two head bolts and replacing with lifting eyes for removing and installing the engine, so GM approves of removing at least two head bolts. They should all be retorqued when you're done.
