A week ago I mistakenly booked three prepaid nights ($90!) at the Santiago Four Points under my name and SPG account, rather than my wife's (she's PLAT now and I'm not anymore). (I thought I was logged in as her to the SPG site, but I was actually logged in as me.) Starwood's 888 number couldn't fix it (or, as they put it, they couldn't "touch" the reservation). Called Santiago and spoke with the property manager (or someone who said he was the equivalent). All three reservations were transferred to my wife while I was on the phone. Going back to the OP--the best idea would seem to be to ask the hotel to just switch the dates in their system. Booking a new reservation and then asking them to cancel the old as was suggested above seems unduly complicated. But that's just speculation on my part...