I have a long-ago booked ticket to go to FRA next week on a personal trip. I may need to cut the trip short and return early. The dates on which I'm looking to return look heavily booked and an upgrade quite unlikely. I have the sense from prior, although limited, experience that it is less expensive to change the return flight once one is in Europe rather than changing it ahead of time? Given that I'm not certain I will have to shorten the trip, I'm considering winging it (so to speak) and trying to change the return segment once I'm in Europe if I need to make the change.

Any thoughts?