With regard to the brown wire and a Mastervolt Alpha Pro regulator: the On/Off control of the regulator _is_ the brown wire. In fact, if the brown wire is not interrupted at installation time via an interface to your engine's ignition key or to an oil pressure switch, then the regulator will always be on 24x7 and it will either burn up the alternator windings or discharge the batteries, whichever happens first. Therefore I agree that yes, it is up to Victron to provide the signal necessary for you to install the relay that will interrupt the brown wire and turn off the regulator. Hopefully the Schneider switch Victron proposes will address your issue.
Non-automated options for switching off the Alpha Pro regulator, short of manually pulling off the brown wire, include:
1. Install an in-line manual switch
2. Set up a "Alternator Off" / "Alternator On" virtual switch buttons on a Mastervolt EasyView screen. This is what I have done. I've never had occasion to need to use these buttons in anger, as the regulator has proven to be 100% reliable with regards to voltages, floats, temperatures, etc., but it is important to have this emergency kill available, just in case.
3. Connect via USB to the Mastervolt MasterBus. On the MasterAdjust software, select the option to "Configure" the regulator. This will turn off the regulator and it will remain off until the configuration is again locked down.