I had a 6 night reservation for May 17 to 23 at VGF, Saturday to Friday. I decided to arrive on Sunday instead, so I called MS this week and changed it to May 18 to 23. No problem, very easy. Hopefully someone here picked up the Saturday night, it was available on the website after I cancelled (lake view studio).
MS can extend (subject to availability) or shorten a reservation by modifying the check-in and/or check-out date without needing to cancel and rebook the reservation.