Thanx for the quick answer! :D
And: I seem to have completely lost my track here.... But I really have no idea how I *SPOLIER* should be able to leave the library (resets the levers) to get a small crowd of characters involved with my brandnew lever-pulling-hobby... Alas!*SPOILER*
Oh wait, sorry! You're still stuck there?! My apologies then, I assumed you got through it/looked up a walkthrough, finished the game and are only talking about it in retrospect.
Forget everything I said then, sorry for the spoilers :(. You can keep the levers down using items you collect - maybe you just don't have the stuff you need yet. If you want the whole solution, let me know what you have in your inventory.