I've already accomplished a similar feat. When I booked my room (almost immediately after tour date announcements) the rate was $129 from the hard rock website itself. They actually charged my credit card at the time of reservation (my experience is that the hotel takes credit card info at reservation and holds it and then charges at checkout... so that seemed odd).

I looked at orbit and the rates (for the same room, same night, et cetera) were like $69. I feel like you can't cancel orbit reservations without penalty whereas I know that I can cancel my Hard Rock reservations up to 72 hours from reservation. This uncertainty prevented me from canceling my room to rebook cheaper through orbit. I checked back a month later and the orbit price went to $79 and lo and behold the Hard Rock rate dropped to the exact SAME $79! I promptly called Hard Rock and asked them to change my reservation to reflect the (MUCH) cheaper rate which they did while I waited on the phone. They did say that my reservation deposit was still going to be held but that the difference would be refunded at checkout.

My plan is similar for when the VAMPS discounted rate is announced. Rather than canceling and then hoping to be able to rebook, I'm just going to tell them that my rate should be cheaper based on the group discount and they should fix it.