Re-alignment/re-positioning of the video map and radar data to extend the life of the tube? The east/west runways would presumably have been exclusively ILS approaches by this time and so it would matter less if the centrelines burned out. But I think 05/23 had SRAs until very late in their operational lives and so being able to see the target as it goes down the extended cenreline would be important - keeping this facility for longer could be achieved by shifting everything E or W slightly. I seem to recall this happening at places I worked when using similar (if not the same) bits of kit.