You can set up multiple ssh keys for any site having multiple user accounts
Below is the example I used to follow in my development for GitHub.com
Config file example
#Personal account
Host github.com-<personal-account-name>
HostName github.com
User git
IdentityFile ~/.ssh/id_rsa_personal
IdentitiesOnly yes
#Organization account
Host github.com-<organization-name>
HostName github.com
User git
IdentityFile ~/.ssh/id_rsa_work
IdentitiesOnly yes
At the time of adding a new origin
For Personal account
git remote add origin git@github.com-<personal-account-name>:<personal-account-name>/<repo-name>.git
For Organisation account
git remote add origin git@github.com-<organization-name>:<organization-name>/<repo-name>.git
Hope it helps.