Why do you want to use a different git repository when you develop a 2nd presence? In my opinion it is not necessary to split that, but instead you should rather make this dependent from other criteria, e.g:
* the 2nd presence is developed by other developers, and they should not have write access to the code of the 1st presence; therefor you have for them a 2nd git repo.
* You share code between multiple AEM projects/customers, and therefor it's easier to push a remote repository to git repositories associated to the multiple AEM projects in Cloud Service.
But you need to be aware, that even if you have multiple git repositories, they will always be deployed all within the same deployment.
The documentation for it: https://experienceleague.adobe.com/docs/experience-manager-cloud-service/content/implementing/using-cloud-manager/managing-code/enterprise-team-dev-setup.html?lang=en