So let's add a new remote called all that we'll reference later when pushing to multiple repositories:
$ git remote add all git://original/repo.git
$ git remote -v
all git://original/repo.git (fetch) <-- ADDED
all git://original/repo.git (push) <-- ADDED
origin git://original/repo.git (fetch)
origin git://original/repo.git (push)
$ git config -l | grep '^remote\.all'
remote.all.url=git://original/repo.git <-- ADDED
remote.all.fetch=+refs/heads/*:refs/remotes/all/* <-- ADDED
$ git remote set-url --add --push all git://another/repo.git
$ git remote -v
all git://original/repo.git (fetch)
all git://another/repo.git (push) <-- CHANGED
origin git://original/repo.git (fetch)
origin git://original/repo.git (push)
$ git config -l | grep '^remote\.all'
remote.all.url=git://original/repo.git
remote.all.fetch=+refs/heads/*:refs/remotes/all/*
remote.all.pushurl=git://another/repo.git <-- ADDED
Based on http://stackoverflow.com/questions/14290113/git-pushing-code-to-two-remotes