The are architectural reasons that this probably isn't something that makes sense for backrest -- though I do agree that backrest needs a good way to share configuration between repos.

I think some sort of templating framework would be a good UI feature and is the most likely solution to this problem, though unsure when I'll budget time for it as it introduces significant UI complexity. In the meantime, editing the config.json and directly copying hooks between repos can be a pretty good way to quickly configure repos in bulk.