Making reservation now/ bounce back offer later?

If I make a reservation for October now and I am going in June, can I apply a bounce back offer to an existing reservation, or do I have to wait and do it all while there in June?

You actually have to book the bounce back offer while you're on property. It can't be applied to an existing reservation (as far as I know). The whole point of the bounce back is to get people to book a new trip not to give a discount on an existing reservation so it would probably be best just to wait until your June trip to book the October trip if a bounce back is currently available.