Well regardless of all these calculations the high at OM add to DA/low at OM disregard is still safetywise safe. If its undereading you will hit the DA at a point higher up on the GS beam, if its overeading you will hit the DA at a lower point on the beam, takes care of all altimeter/ISA/temperature errors all at once. Dont know why they changed it actually, there was always scope for temperature corrections in the AIP.
These questions are useful actually as they highlight things you thought you knew then look at the books and realise the Airservices NAZIS have changed it years ago...
