Use a secondary Github account

Create a new pair of keys

ssh-keygen -t ed25519 -C "your_email@example.com"

This will generate a file in ~/.ssh/ (eg id_ed25519). Add the .pub in your profile’s Settings/SSH and GPG keys.

Edit .git/config to add:

sshCommand = ssh -i ~/.ssh/id_ed25519

How to merge two Github accounts

Short answer: it’s not directly possible to merge two accounts. However, it’s possible to transfer repositories and most of the ownership of the commits.

Transfer repositories

For each repository, go to the repository’s Settings, scroll down to Transfer ownership, fill the form with your other username, and accept the transfer by clicking on the link you will receive by mail.

Transfer (most of) the commits

Go to your profile’s Settings, select Emails, add a new email (your gmail with a +suffix works), and delete the old email. Go to the other account and add the email there. When you do it, most of the commits will be attributed to the other account in regards to the contributions’s diagram on your front page.