I would be arriving two days later, departing the same day as the original reservation. I spoke with a different customer service person today, she explained (as expected) that in order for them to change the reservation they needed to cancel and rebook, and since it was sold out they would be unable to rebook. She said that she could contact the hotel directly as they would have the ability to modify my reservation and hold the room that I already had reserved in order to accommodate the new reservation (fingers crossed). She said I would get a response within 3 business days.