Working on robots between regionals

Does anyone know if it is legal to work on your robot between regionals? My team is thinking of attending both the Silicon Valley Regional, and the Sacramento Regional next year, and we have no idea on whether we can work on our robot between regionals. If we can't, what do we do? We have the new rookies asking questions about that, and even we don't know the answer!

I hope this isn't an obvious question. I already searched for it in the search query, but I found nothing.

Thanks!