I would only expect the airport to do that if your original flight is oversold and your free change potentially saves them a voucher for compensation. Most of the time they have to follow the rules about SDFC the same as you do. Sometimes this can even trigger in app or online via email as an offer to swap your flight around.

But if your direct flight is not oversold I do not think an airport agent would be able to do anything for you that a phone agent could not.