Bushy,
You are correct … CASA vary their approach from region to region with little standardization in between. I have also had your experience with ops manual but in fairness to the CASA folk involved they were suggesting alteration of the ops manual to reflect the procedures used. We had streamlined one of our processes to something more workable amd the variation was detected in a surveillance.
Chimbu,
Would not your EGT system involve an STC and an AFM supplement? Over the years with modifications on older aircraft; RNAV systems, payload increase and single point refueling spring to mind, the STC was accompanied by associated checklist items that had to be incorporated into the aeroplane manufactures checklist.