Yes, you can add it on when the code comes out if there is availability at your resort. They only allot so many rooms per resort that will be eligable for the FD promo. The info should be released in early April and will be available to book first by Disney Visa holders for the first 3 days, then it will open to the general public. If you add the code during the first three days then you shouldn't have a problem, but if you book after that there is always the possibility you will have to change resorts or change your dates.