It is still possible for the Swan and or Dolphin to pop up on PL/HW at a great rate. The Swan was just on PL for $251 for 11/4-11/7 three days ago. An OK rate but it has been much lower. The key is how their bookings are going for any period. As a reminder, hotels use PL/HW to fill empty rooms.
To prevent the loss of your FP+, just make sure to link any new overlaying reservation to your
MDE before canceling your original reservation. The alternative is to just wait until you are within the 30 day window of your arrival and then your hotel changes can't have any impact in your FP+.
Dave