I had Royal Pacific Hotel (RPH) reserved for 4 nights room-only (June 17-21). I called to change arrival to June 19 and length of stay to 2-nights (June 19-21). I was told that the "system" wouldn't allow any arrivals for June 19 at the RPH, so I had to book at the Hard Rock Hotel for a slightly higher rate and cancel the RPH reservation.
I've never had a problem at any hotel with changing my reservation when its within the time period of my original reservation and prior to the cancellation date cut-off.
I thought about calling back later, but the availability of the discount I'm getting is limited and I didn't want to chance not being able to get it at all. 

I've never had a problem at any hotel with changing my reservation when its within the time period of my original reservation and prior to the cancellation date cut-off.

