If you're not on a package you shouldn't have a problem. Last year we had booked eleven nights but changed it to eight nights. I called CRO and made the change, but it didn't get to the hotel. When I checked in I noticed they had us staying eleven nights. I told them at the desk we'd be leaving after eight nights and that I'd made the change through CRO. She said the best thing to do would be to stop at the front desk on the day we were leaving and tell them we were checking out early. That's what we did. No problem.