Hi George,
Congratulations on receiving your invitation to the second stage. Just in case you don't manage to swap your date most universities have a withdrawal cut-off dates where you get 100% refund on your fees. I think in most cases cut-off period 1 (where you will receive a 100% refund) is on or around the 1st of October. I'd check with your university to find out their withdrawal cut-off dates.
DC