Its my understanding that if you are issued travel funds between March 1 - June 30, 2020, then it will be extended. So if you cancel a flight or re-book a cheaper flight leaving you with a credit, you will receive the expiration extension on those travel funds As long as you cancel the August flights before June 30th, you should be eligible for the extension.
Flight changes are subject to the same expiration date as travel funds would be, which is the original purchase date under normal circumstances. As of now, you could re-book for any flight prior to your mid-March original purchase date. Once you cancel and the June 2021 expiration date is rolled out, you could re-book for any flight prior to June 30, 2021. But you would not be able to re-book for anything beyond June 30, 2021. Re-booking rather than cancelling is advisable for a couple of reasons - for one, you won't lose your early bird check-in if applicable. And two, when purchasing new flights, you're capped at using two travel funds per purchase. Each person on the reservation will have their own travel fund(s) to use, so its possible you'd have to book people separately if booking new flights using travel funds.
