@John-Michael5
Yes, it is possible (regarding check-out date: can also be changed during the reservation. If it is an extension, it must be confirmed (by the host!) at latest before the check-out time on the check-out date).
But always keep in mind the host must accept the change, which can take some time (and is not an obligation !) Many host will not be pleased if you (want to) change dates on a very short notice.