Apparently the Leave supporters were so distrustful of authority that they were taking pens to mark the ballot papers[0], so retrospectively changing the rules would be like trying to put out a fire by throwing on petrol.
Unfortunately the former United Kingdom has shown it is irrevocably divided, so should get on with trying to make the best of a bad situation, e.g. (in my view) by setting up an independent Scotland and independent London[1].
[0] http://www.standard.co.uk/news/politics/brexit-backers-urge-...
[1] https://www.change.org/p/sadiq-khan-declare-london-independe...