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It has, yes. Apart from many roundabouts and town centre alterations there's bridges cutting corners on the coast in Scotland (there is a new road on Helmsdale which is about 1 mile SHORTER than before) as well as the finish line (The old finish line at JoG is no longer there. The old hotel is now private flats. The new finish point is the leading edge of the mini roundabout about 68 yards BEFORE what was the old front door.). John Taylor's LEJOG book goes through some of the course change details in documenting the attempts over the years.
They're already done similar with LEJOG
The roads change and I think they have a new finish because you can no longer ride all the way to the hotel wall or something at the top.
The routes are basically along motorways now though so without follow vehicles, training for them is quite a stressful exercise. With Mike's death weighing on my mind, personally, I'm even less inclined to do this kind of thing again.