As long as your new check in date is covered under the bounceback dates, it won't be problem. I've booked bounceback deals, then changed the dates and even the resort without a problem. In fact, I currently have a bounceback trip booked for Nov 27th-Dec 4th that I changed the resort and dates for a few months ago. My only problem was that I really needed Nov 26th-Dec 4th and the bounceback deal that I booked when I was there last May did not cover Nov 26th. When I switched dates, I had to book Nov 26th as a room only at full price, then when the AP discount came out I switched that first night to the AP discount. The bounceback covered every night of my new dates, except that first night. If I had booked the trip as just one stay, I would have lost the bounceback discount, because it wouldn't have been in effect at the time of check in.