I can't speak for the Spanish CAA but there are many ways for the rules to be implemented - not just in legislation.
If the Spanish CAA has insisted that aircraft operators put this in their Ops Manual and somewhere else has a rule that says the aircraft must normally be operated in accordance with the the procedures in the Ops Manual - then so be it.
If I understand you correctly we are talking about the aircraft operator's Ops Manual - in which case it will be the commander's responsibility (there will be a rule about that somewhere too). I don't have Doc 9137 to hand but the authoritative document will be Annex 14 and I think that still includes provisions for reducing RFF cover where there are less than 700 movements in the previous busy 3 months. But remember, Annex 14 says what the aerodrome has to do (in order to get certified), it's the Ops Manual that determines how the crew operate the aircraft - and I believe there are many examples where the Ops Manual is more restrictive than the ICAO SARPs.