Adding commits to another person's pull request on GitHub

As long as the original author has clicked the checkbox in the bottom right:

If that box is checked, then you can push back to the original branch without needing to add a remote by using:

git push [email protected]:user/repo local_branch_name:remote_branch_name

This is particularly useful if you're using a tool like hub where you can check out a pull request without needing to add a remote.

It is possible to do this now (link)

Suppose you have received a pull request in yourrepo from otheruser.

Add the other user as a remote

git remote add otheruser https://github.com/otheruser/yourrepo.git

Fetch

git fetch otheruser

Create a branch from their repo

git checkout -b otheruser-master otheruser/master 

Now make some changes and commit. Push to their repo

git push otheruser HEAD:master

Not unless barryceelen gives you push access to his fork. You'll have to close his pull request and open a new one from your branch that includes his commits.

Not being able to do what you want to do is annoying. To make better use of GitHub flow, I'd suggest asking forkers to open issues separately from their pull requests that solve them, meaning you can keep the initial conversation flow and have it closed by whatever pull request you decide as the best.