FRUSTRATED. How to drop the firearm charge to a lesser charge?

My son is in jail and has been for the past 9 months. He was convicted of Grand theft and the sentence was appealed. In the mean time he had an altercation at his apratment. The law officer that responded asked him if he had any weapons. He produced his hunting shotgun and was then charged with "Felony posession of a firearm" since he was a convicted felon. In Virginia this carries a two year mandatory sentence. Since then his appeal was granted and the charge was reduced to petty larceny. The problem is that the commonwealth attorney is not willing to drop the firearm charge to a lesser charge. He says "at the time he was a felon". Is there anything we can do at this point? His court appointed attorney seems to just go along with whatever the commonwealth attorney says. Any suggestions would be greatly appreciated.

Get private counsel to thoroughly brief the point and argue/negotiate more forcefully with the Prosecutor. The public counsel just do not have the time to do so very often, unfortunately.