Yes, it’s possible to back up only select repositories.
By default, BackHub creates backups of all repositories it gets access to. If you want to back up only select repositories, you can simply limit access to those repositories.
In the installation dialog, you choose whether to give access to all repositories, or to only select repositories. Choose “select repositories” and enter the names of the repositories to back up.
If you have already installed BackHub, you can edit the permissions by managing your installations on GitHub.