Originally Posted by
diesteldorf
Try making another reservation to use the new $300 credit. Wait until you get the $300 credit. Then go back and modify your $200 reservation, or cancel and rebook immediatly for the new dates. If you book/modify immediatly AND have already been credited for the new $300 credit, there is a chance they will NOT claw back your original $200.00 credit.
Good Luck.
If you cancel, Amex definitely will claw back $200. You can change dates on an existing reservation but it can be messy given that you are fiddling around a prepaid stay by Expedia.