So I canceled my delta comfort plus ticket that was supposed to fly next week because conference got canceled. Seem I got a full credit using the same ticket number. My question now, if I use this credit to buy a new ticket let's say for late May, will I be able to change/cancel it for free again? Or because it's a different pay system (not a real payment) and/or already got the cancelation fee waved first time then I cannot do it again? In case I can, what is the deadline for free changes?