[danillonunes]

Yes, you can run in your local git repo:

  git config core.sshCommand "ssh -i /home/your_user/.ssh/your_custom_key"

(I believe replacing "/home/your_user" with "~" works too)

I use this all the time as my main key is ed25519 but some old repositories only support rsa keys.

The sshCommand config is, as the name says, the literal ssh command that is used by git when operations that call a remote with ssh (usually push/pull). You can also put other ssh options in there if you need.

Another option to achieve the same effect is to setup directly in your ~/.ssh/config:

  Host your_custom_alias
    HostName git.domain.com
    User git
    IdentityFile ~/.ssh/your_custom_key

then instead of "git clone [e-mail]:repo.git" you clone it with "git clone your_custom_alias:repo.git" (or you change the remote if is already cloned). In this case you don't need to have to change the git sshCommand option.