Yeah, I understand that with QNH from a METAR or a TAF, you're not going to be able to take the 100ft off the minima, but the AIP suggests you can't use the METAR QNH AT ALL. It lists 3 sources of QNH that need to be set prior to passing the IAF, and METAR QHN isn't one of them.
I'm curious as to why that's the case.
Could it be an unintended consequence of a sloppy wording? i.e. it can't be used for "a. the actual aerodrome QNH from an approved source" (for the reasons above) but
should be covered by "b. the forecast terminal QNH" even though it isn't a forecast. Maybe someone simply forgot a METAR isn't a forecast when writing the rule?
edited to add "automet" might be an AUTO METAR?