The ssh address registered with git remote probably already include the user name, so you would need to use a complete ssh url like:
otheruser@remote:arepo
That won't work, because ssh will use the default public/private keys (currently used by the first user for authentication).
You can register a new remote in your local config:
# use the current ssh address registered for origin, changing just the user
# but you need a config file
git remote add originOtheruser otheruser:arepo
You must have a $HOME/.ssh/config
file, in order to define the ssh entry 'otheruser', because ssh needs to know what public/private key it needs to use: it cannot be the default ones ($HOME/.ssh/id_rsa
and $HOME/.ssh/id_rsa.pub
)
See for instance "how to add deploy key for 2 repo with 1 user on github"
Host otheruser
HostName remote
User otheruser
IdentityFile ~/.ssh/otheruser
That supposes you have stored the public/private keys for otheruser as:
$HOME/.ssh/otheruser
$HOME/.ssh/otheruser.pub
Now, you can use that new remote to push:
git push originOtheruser master