Originally Posted by Jaimito Cartero
I know that whenever I change a reward ticket, the miles are redeposited into my account, and then taken out again. From this, I'd say that if change it, you'll be charged the difference.
That has been my experience as well. Miles and taxes are redeposited and the miles, fees, and taxes are recalculated based on the availability of the new dates. I am 100% positive that a change (past Mar 05) to later dates requires the new charges/levels.
However, booking before the effective date (Mar 05) for a flight past this date triggers the old charges.