Hi, Misty!
The short answer to your question is a resounding "yes!"
Guests who book their Walt Disney World vacations directly through WDW may cancel their vacations with no penalty if cancellation is made at least 6 days prior to arrival. A Cast Member explained to me that, should a situation such as those described in your question occur, the Guest can simply contact WDW, book the new vacation and cancel the old one. Any deposits made will simply be credited to the Guest, who would then make the new deposit on the second package.
It's a win-win, really, in that you get peace of mind knowing that you have the package / resort you're looking for, yet have the flexibility of securing a
special offer should one become available closer to your arrival day. Great, isn't it?
Send more questions as you think of them, Misty! We love to help!