It would be a shame if thousands of people forked the listed repos and gists…
Any centralization is fragile. Github is more fragile than what is possible, but there is little point on improving that.
I'm sure that you could rm the .git/ and overwrite it but keep it pointing at the same repo. I don't know what would happen on the remote, though, when you push.
For good measure, you should also probably run a `git gc` (garbage collect) on the repo too, just to be sure. :)
Not from my computer.