backup your codes.
git clone https://github.com/NodeBB/NodeBB.git
switch to tag that you modified from. Perhaps, v0.4.3? e.g. git checkout v0.4.3
rsync your codes to the clone.
git commit, git tag my_tag, git checkout master, git merge my_tag
You may have to solve conflicts by yourself.
I doubt this has been explored at all, since this being a forum software in general and not something like Google Docs or any other collaborative software out there in the wild. I would like to see it as something Discourse has with there "Wiki Posts" but I won't suspect it to be even a low priority for the devs.