Making changes to a Priceline reservation after the check-in date can be quite complex. Generally, once a traveler has checked in, the reservation is considered complete, and options for modifications become limited. Most hotel and airline policies dictate that changes should be made before the scheduled check-in. If you require changes after this point, it is advisable to review the specific terms and conditions associated with your booking, as they can vary depending on the provider.
For hotel reservations, most establishments do not allow for modifications or cancellations after check-in. If you find yourself needing to change a flight reservation after check-in, it may depend on the airline's policies, and you might find yourself facing additional fees or restrictions.
For more specific guidance based on your individual reservation, it would be beneficial to check the original confirmation details provided at the time of booking. They may include information on policies regarding changes. Additionally, visiting the current Priceline web page will give you access to customer service options where you may find more assistance or clarification regarding your situation.