Just replace with another  pcm  from the same year mustang with the same calibration number, make sure the axle ratio pid shows the correct gear ratio, gain 10 minute security access to Access PATS functions, erase PATS keys in used PCM  and reprogram all the existing PATS keys

 once security access is granted click on parameter reset  or it will never start, choose pcm replacement when prompted. 2  keys are needed.