Some of this has to do with the rules of the RV park or state park that the reservation is made at. I can tell you that this will not fly for a Wisconsin State Park. You either use the reservation or you don't. For years people would make reservations at WI state parks up to the max of 21 days just to get a particular weekend. Yes, they would actually pay a small fortune to get a desired site for a few days. That would leave a paid for, but unoccupied site sitting unused for a couple of weeks at a crack.
So WI put a stop to that. If you don't occupy the site within the first 24 hours, you lose it. If you leave early and you let them know ahead of time when checking in, they will refund what you are not using. But you cannot "share" a reservation.
Being that we don't know the rules for the particular park you are asking about, you'll need to call RA and ask what you can do. More than likely if your friend is present they will alloy you to change your reservation and then let your friend make his. They've done that for us once before. However, what they do is cancel the ENTIRE reservation, then re-reserve the time you really want. They warn you that someone else could get your time in the few minutes that they are doing this...
