In most cases the regulator,to provide low pressure in a system has its own presure relive valve.So most people using low pressure systems are safe on that acount.(if they didnt fiddle with it)
Combined with the commercialy available 1000psi PRD with a 1/4 bsp tread,most regulators can be modified with that, just replace the bottleside clock for this PRD.

Now for the pure Full pressure users this commercial PRD is not difficult to be fitted in the system,anywhere between the bottle and the first valve in the system is more than adequate.Nothing more that a T adaptor.

Another ,and more interesting question.How are the technicals going to test this PRDs?