SASless
No, this isn't a CAA specific requirement, in all authorities the requirement for the aircraft to be kept to the Manufacturers TCDS is the same, just some authorities tend to turn a blind eye

, but ask any authority to put it in writing that it is ok to fit Bell to Agusta and vice versa and see what the response is.
Both Bell and Agusta have issued letters stating NOT to fit each others parts.
The reason these are being affected as much now, is the ARC (EASA Aircraft) procedure, where the maintenance company issueing the ARC is
responsible for the Continued Airworthiness of the aircraft and if the incorrect parts are fitted, their heads be it
The CAA do a grand job in keeping our skies safe

albeit abit infuriating sometimes