Some googling with appropriate terms (such as RFM, AOC, EASA etc) brings up lots of useful stuff for you. This Australian CAA (CASA) link states fairly conclusively how supplements should be approved (by them) and is a common standard with all NAAs:
Civil Aviation Safety Authority - What is an Aircraft Flight Manual supplement?
You will also see the AFM/RFM specified in the TCDS as the basis for operating, and - as has been stated - they form part of the AOC.