forget, I take your point. However, the need for an AEO is, from my experience, absolute. For example, at an overseas base, we got airborne and a snag appeared. The first time the symptoms appeared we took action iaw the checklist, but that did not cure the fault. My highly experienced AEO diagnosed a cable fault as being the most likely explanation. This was po-poo'd by the engineers. Bits were replaced and the thing recurred once airborne again. AEO went through the red book with engineers trying to convince them that he was most likely right. Again ignored and more bits fitted. Failed again - that left only the loom to be replaced. When the new loom + lecky arrived and started work, they soon found that the original cable was virtually dust - it was one of those components that was lifed to the aircraft life, therefore never examined, serviced or replaced; and with the aircraft flown to over 150% of its planned life....
The CAA would probably have no difficulty with some modern kit being installed, provided it was done by BAe and they were fully involved throughout the design and installation. I will accept that you could probably get away without the navs; however, for reasons above - definitely not without the AEO...
As for the air conditioning, what was the figure at Akrotiri in summer? Airborne within 30 mins of cooler out or scrub??!! (It was 10 mins in Canberras). Temps in a hot-soaked cockpit measured at over 130 deg F. I rest my case!