I just flew with 4 others on 5 separate United award reservations.
We had a flight scheduled from LHR-FRA-JNB - and wanted to change it to a direct LHR-JNB flight on the day of our flight. Using the United call back number, they wanted to charge me a $75 change fee. Calling the regular United number, they did it for free. (we had to do it one at a time. They weren't showing availability when trying to do more than one at a time)
Just sharing in case this might help someone.