@Biljana35 Whenever a guest has asked to move their dates outside of the cancellation policy window, I always just call Airbnb and have them do it. I ask them to do it in such a way that the existing cancellation conditions still apply to the new reservation. They have always been understanding and happy to do this for me. This pertains to short-term stays, but I assume they would also help reschedule long-term stays with the original policy intact.
As far as allowing/disallowing the change into lower season rates, I would just change the rate for their desired stay into the rate they had previously, and I would only do this if the chances of booking the old dates are relatively high. I normally don’t allow changes at all less than 2 months before the original stay in Maui, since Maui guests tend to book months in advance - not very many last-minute bookers, so chances of rebooking last-minute cancellations are low. Greenville, however, gets a lot of “let’s get away this weekend” bookers, so rebooking would be more likely. Think about your location and its market before making a decision.
By the way, I have to say that if possible, I try to accommodate guests with these requests within reason. Denying these requests essentially causes the guest to feel compelled to come, and I really don’t want guests staying at our place who don’t want to be there. You certainly are within your rights to be strict with your policies, but on a case-by-case basis, good will should also be kept in mind.