Hello again! I investigated this as part of our new panel update (8.4), but unfortunately I have bad news.
The means that we have of changing these values are unreliable at best. Setting the cruise altitude, flight number or any similar variables does not automatically trigger the ATC to make recalculations. Sometimes the ATC does register the change, but only after proceeding through the first portion of your flight. It’s hard to determine exactly when it picks it up, but it could be in the transition between what the simulator considers to be your “departure” segment and the “enroute” segment.
We don’t have enough control over this to make something useful, if we included this feature currently it would seem broken for the majority of those who tried it. I will keep a look out, and if I find a reliable way to implement this I will take the first chance to do so!
Sorry for the inconvenience.
Kind Regards,
Malte