According to Booking.com policy, if stay is extended with a few nights, Booking.com should only add the price for the additional nights according to the current pricing in the calendar and leave the remaining nights as per original booking.
If the stay is shortened by a few nights, Booking.com should subtract the price calculated as per channel reservation price breakdown. The remaining nights should remain as per original booking.
In a situation, where the stay in moved to an entirely different period, an entirely new price should be calculated by the channel.