From dim and distant memory I seem to remember there was a desensitising programme for hayfever. It was along the lines of desensitization for motion sickness.
Certainly once you have a price on your head (aircrew training) the system used to move heaven and earth to retain your skills. I remember one Vulcan captain back in the 60s who suffered a collapsed lung. Had his lung reattached to his rib cage and was cleared to fly multi-crew cockpit only. Made wg cdr and is still around and kicking.