For your first point, does ../../user/repo.git not work? I have a self hosted GitLab and that’s how I’ve specified all my submodules and it survived a top-level

For your first point, does ../../user/repo.git not work? I have a self hosted GitLab and that’s how I’ve specified all my submodules and it survived a top-level url change (with a new clone or changing the origin)