Lemper, most of what you said makes sense. I have no idea what the "alert height" is though
And do not forget that if the airport is declared Cat III, and the RVR increases to Cat II or even I, no one under Cat III authorisation will be cleared to approach; one of the main reason being that in Cat III, the VASI/PAPI are switched off. Why would that be?
No idea, something to do with their inaccuracies at low altitude and the possible distraction of seeing 4 reds or 4 whites at DH?
If the crew were refused an approach due to a change in VIS/Cloud base, could they declare a new category of approach provided they haven't passed the IAF?