That's like spam. Pick your best idea and apply with that, if that does not get in then you need a better one or a better team. It's up to you to pick your best idea, not up to YC, after all it's not as if you're going to be executing on all of your ideas at once and the YC crew has too little time during the evaluation of all the applications as it is.

If they'd allow someone to monopolize the pipeline it would be grossly unfair to those that do apply with just the one idea that they ideally would be executing on regardless of whether or not YC accepts them.