The soldier's nationality is irrelevant. If they are serving in a Greek detachment, which in ARMA III's case they are, as it takes place in the Greek islands of the Aegean sea, they MUST follow the detachment's rules. A British soldier won't follow British army protocol while serving in a Greek detachment. They will follow Greek army protocol. Otherwise, it would be insubordination.
Please stop trying to counter this point with baseless accusations.