In the past, I have been able to get a change fee refunded, after the fact, when I cancelled a trip on (say) day X and a travel waiver was issued for the trip dates on (say) day X+1.

I called and asked an agent to do this over the phone, and they basically filled out a refund request for me — same thing you can do online on the UA refunds request form. The time period of the flight was covered by the travel waiver.