We've done this, no problem.
Reservations CM said to put the phrase "Continuing reservation" on the notes for your reservation. Call reservations and have them do this for you. The room assigner at the resort should see this note and try to keep you in the same room.
Also, when you check in, remind them again that this is a "continuing reservation" and if at all possible, you'd appreciate being able to stay in the same room.
You will have to go to the front desk before check out time on the switch over day and handle the paperwork.