You probably would only be able to change to May BB dates if there is another BB that opens up later that includes the May dates you want, and probably couldn't get FD, but a room discount as you mentioned. DISers have posted booking during one BB and trying to modify to the dates of another BB but there have been mixed results - some people were able to modify their BB res no problem, while others were told "no way".
Based on previous years, the next years BB dates usually come out with a BB starting around November, so I guess if you have the extra $ to deposit and then are willing to see what happens, you can always go for it

Book something with the BB dates available to you when you are there, and then keep watching here on the DIS for someone to post the next BB and see what dates are on that one. Then using that info, try and modify. At least you will always be able to cancel and receive a full refund as long as you do so based on the cancellation terms of the original offer.....
If you do it, be sure and post here on the DIS about how it works for you!