In my experience it can also work like a reset button on a computer - restores a stable known state in favour of the plants. This does have to be combined with root cause removal and a massive clean up, of course.I always looked at the blackouts like using an atomic bomb to kill the mosquito. Blackouts/chemicals/erythromycin etc. will only remove the effect, but not the source/cause of the problem.
Re siphoning: I think if you calculate how much Blue Exit you dosed per litre so far you could put it back in if you siphoned out what BGA you can. I presume Easylife don’t advise that because not every customer is going to be able to correctly figure that out!?