Can "accept all changes" by reversed?

I'm sure some of you have seen the problems that the UN have had with
MS Word documents today!

A friend had a question - is it possible to undo or reverse "accept all
changes" in a Word document so that you can see the change tracking
again? I'm wondering if the changes are deleted from the file entirely,
or just hidden and possibly viewable with (say) a third-party app?