JW411, your Corporal Jed was hardly the only bod who could set up bleed valves. There were plenty more on LSS at Brize who could do it on a dark freezing cold nightshift.
I was sent on an engine change at Gan (364 I think? I have photos) and on completion we had to do all the settings. The Rolls Royce graphs in the MM went from minus 30C to plus 25C. The lowest temperature ever recorded at Gan was 27C during a tropical downpour about ten years earlier, so we had to interpolate the graphs. It took four days of doing the trim runs at 2am when it was coolest to get the trims right and despatch the aircraft. (It was on a max load, carrying depth charges to Singapore)