Yes, but there are two things that will determine it:
1) Whether there is availability for the discount in your specific resort and room for your dates and
2) Whether you are booked as a room only or a package
If there is availability for your specific resort (including specific room and dates), they will apply the discount. That means that if you are booked as a room-only (not a MYW package), you can apply a room-only discount, if that discount is available for your room and dates. If you want to change from a room only to a package that includes tickets or tickets and dining, you will have to rebook. If you want to change from a package that includes tickets or tickets and dining to a room-only reservation, you will also have to rebook. At least that's how it was in 2012. HTH!