Originally Posted by
Ross0
+1 I haven't tried it, but did look into this exact issue a few months ago and was told this is the only way it can be done to avoid the full r/t reprice.
This is not only the case for award tickets, by the way.
In general if you make changes to a ticket before you start travel, it's repriced according to the fares when you make the change. But if you make changes after travel has started, it's repriced according to historical (time of purchase) fares.