Priceline will tell you that their name-your-price reservations are non-changable, and if you call them requesting a change to a reservation they will tell you the same thing.
However, my father (a Priceline Pro) passes along this info: if you need to change a hotel reservation, don’t call Priceline, call the hotel directly. He’s found that they are nearly always willing to work with him to change the reservation for no fee. Sometimes the hotel is happy to have the room back to sell at full price. Whatever the reason, he has found nearly every hotel to be accommodating to changes in date.
Same goes with car rentals — he has called car rental companies and they have been happy to change dates on a reservation.
It’s a small thing, but if you need to change a Priceline reservation, all hope is not lost — call the provider directly and ask nicely.