$ git remote add theirusername [email protected]:theirusername/reponame.git
$ git fetch theirusername
$ git checkout -b mynamefortheirbranch theirusername/theirbranch
git commit --amend --author="xxx <xxx@xxx>"
$ git remote add theirusername [email protected]:theirusername/reponame.git
$ git fetch theirusername
$ git checkout -b mynamefortheirbranch theirusername/theirbranch
git commit --amend --author="xxx <xxx@xxx>"