And if that's not enough, Eric S. Raymond has written a bunch of absurdly powerful tools for scenarios like this one:

http://www.catb.org/esr/reposurgeon/

https://gitlab.com/esr/git-debubble

https://gitlab.com/esr/git-weave

Some background information provided by ESR, in addition to what you can find on the homepage:

https://groups.google.com/forum/m/#!topic/golang-nuts/WstriK...

https://news.ycombinator.com/item?id=22304131