My earlier reply was thinking about the AEC Z figures using the old Ford style regulators with separate OV module.
The 2 stage switch shown in the Z figures for the B&C regulator, or a separate alternator field switch, or a pullable CB, would all accomplish the shutdown of the alternator. So your choice on how to implement.
The 2 stage switch should be the simplest from an operational standpoint; hit one switch and everything (except battery bus items) goes dark. When the 2 stage master is off (all the way down), it disconnects the master contactor *and* opens the circuit to the regulator, killing the power to the alternator field. One click up powers the master but leaves the regulator (alternator field) unpowered. Full up brings the regulator & alternator on line.
Charlie