Originally Posted by
BOSTransplant
Within 24 hours, you can do a same day confirmed change for free IF there is the same fare class available. I'm almost 100% sure you won't be able to find that fare availability, so you won't be able to do it in Y.
Why would you say this? Do you have access to the fare bucket data? Remember the fare class must be open but it doesn't have to available for sale, mostly due to advance purchase requirements.