Originally Posted by
HiAperture
No way to do what you are saying, book a round trip but only tell the airline when and where you want to go on one leg, you will have to tell them both legs at the same time. You will have to look at the fare rules for your trip, usually 6 months is the max. You can always just pick something random and far out in dates, then pay to change the second leg later, but there will be change fees and fare differences at that time.
Often with incredible after departure fees and pricing differentials enough to choke a horse. Or render the change moot due to the ridiculous price.
Might be cheaper to buy a new less expensive round trip back and drop the return vs. pay to change after departure. Or the original R/T in case the date is OK and a one way with no change fees.
I think any choice meant to disrupt the original R/T price is doomed to fail.