@Arnie89 Anything you change only affects new bookings, not confirmed reservations, which are governed by whatever was in place when the guest booked. This could be cancellation policy, house rules, amenities, anything.
So if, for instance, you decided to change your check-out time from 11 am to 10 am, a guest who booked before that would still be able to check out at 11. Or if you decided to no longer offer washing machine use, and removed the machine because guests were abusing it and broke it, you would have to let an already booked guest know that and either offer to wash their clothes for them, offer a discount for the missing amenity, or refund them if it was a deal-breaker and they wanted to cancel.