[ruxkor]

If I recall correctly, it is possible to modify a pull-request by deleting the "active" commit of the pull request on github and adding something else, i.e. if I do something like rebase -i and then a push -f (which I can, because, after all, it is my own repository I am pushing to.)

[judofyr]

The point of this article was that you can use a SHA1 in the pull-request dialog. Because no-one can change a SHA1, it's pinned to that specific commit.