An A&P can't sign-off any avionics repair.
An A&P/IA can't sign-off any avionics repair.
An A&P/IA with FCC GROL + Radar can't sign-off any avionics repair.
An A&P/IA with FCC GROL can't submit an 337 on an avionics repair.
Only an "approved facility" with the approved capability can.
Nothing...