It seems that a lot of people are confused about having an already existing reservation or not and modifying or adding when the
Free Dining is released.
If you have a current vacation booked, it means ABSOLUTELY NOTHING as far as getting free dining! You're no further ahead or behind anyone else who's trying to book the Free Dining as well.
The Free Dining rooms are a set number of rooms per resort and per category. That's it. Whether you already have one booked or not has nothing to do with whether you'll be able to get one of these designated FD rooms.
Some people book ahead because they know they're going one way or another and want to guarantee their room. That's fine.
Others book ahead, thinking it will give them an edge when free dining comes out. It DOESN'T. You still need to go online or call to make the modification or make a new reservation. And if the FD rooms are gone before you do that, they're gone. Doesn't matter if you already have a reservation or not.
And even others wait until the FD promo comes out because they're flexible in dates/resorts so they might as well wait and see what's available. That's fine too.
Just understand that having a pre-existing booking does not increase/decrease your chances of getting Free Dining.