create different ssh key according the article Mac Set-Up Git
$ ssh-keygen -t rsa -C "your_email@youremail.com"
Please refer to github ssh issues for common problems.
for example, 2 keys created at:
~/.ssh/id_rsa_work
~/.ssh/id_rsa_personal
then, add these two keys as following
$ ssh-add ~/.ssh/id_rsa_work
$ ssh-add ~/.ssh/id_rsa_personal
you can delete all cached keys before
$ ssh-add -D
finally, you can check your saved keys
$ ssh-add -l
$ cd ~/.ssh/
$ touch config
$ subl -a config
Then added
# work account
Host github.com-work
HostName github.com
User git
IdentityFile ~/.ssh/id_rsa_work
# personal account
Host github.com-personal
HostName github.com
User git
IdentityFile ~/.ssh/id_rsa_personal
clone your repo (note "github.com-personal")
git clone git@github.com-personal:work/repo.git repo_personal
cd repo_personal and modify git config
$ git config user.name "personal"
$ git config user.email "personal@gmail.com"
or
$ git config user.name "work"
$ git config user.email "work@gmail.com"
then use normal flow to push your code
$ git add .
$ git commit -m "your comments"
$ git push