What?
Amadeus Altea (Res system AFKL uses) and Amadeus Altea Airport (The DCS - Departure Control System) allow you to change the FF numbers as many times as you want (until the flight finalizes in the DCS).
I just coordinate flights and book them on the airline’s website. I am not a travel agent that understands Amadeus. I did contact KLM and Delta but neither airline was able or willing to change it back, all KLM said was that they will check into it. But thanks for your insight.