They will allow a free change if there is a significant schedule change (and a full refund if it is big enough) or within the 24-hour purchase window (as mentioned below). Other than that no changes (although I notice TATL on AA can be changed for a fee) and no credit at all for future flights if you cancel. Not sure if AA is the same as DL which won't even let you cancel online (although I suspect an agent could do it). If they were to allow you to cancel and apply the credit to a future flight, that would effectively make them changeable and more valuable than the non-refundable main cabin fares which carry a change fee.
Last edited by xliioper; Jan 1, 2020 at 2:20 pm