Photos (beta) for Mac

So i have two different iPhoto libraries, a main library, and a smaller ancillary library on another mac. I upgraded both yesterday, which included the new Photos app. However, the ancillary library synced with iCloud before the main library had a chance to. Is there anyway to change the main library that syncs to iCloud to my other iPhoto library?

I am hoping to avoid a trip to the apple store, but wanted to ask here first.

Thanks