OK, so maybe I'm going to be worng again but here goes.
Firstly, I agree that swapping an EPIRB from boat to boat is a bad idea and I acknowledge that it takes very little effort, especially in the US where it can be done on-line, to change the details of the EPIRB. But . . . .
I thought the SAR people always
called the contacts on the registered list to advise them of the apparent emergency.
If this is so and the EPIRB you're borrowing belongs to you (your boat, your list of contacts) then it stands to reason that your family will get the initial call.
So, having said that, is it also not likely that if you family knew the situation they would be able to advise the SAR that the boat is different but that the emergency is probably real? The number of people on board is moot because that will change every time the boat leaves it's berth (at least it will on mine
) and AFAIK
that is not a piece of data recorded against the EPIRB.
So if the chips were down and the choice was to leave without an EPIRB or to leave with one that had the wrong details, I may take mine with me, having first advised my "contacts" of the detail changes. What I would do is task my "contacts" with updating the EPRIB details in my absence as soon as possible.
In NZ, the details of an EPIRB can't be changed on-line and AFAIK
the office that does change it works office hours so the chance of the dilemma happening here is probably greater than in the US.