The easy answer would be on some non-production copy of the Rails app, point at the new db in database.yml, and simply run `rails db:create; rails db:schema:loa

The easy answer would be on some non-production copy of the Rails app, point at the new db in database.yml, and simply run `rails db:create; rails db:schema:load`, or some variation rails command like `rails db:prepare`. Rather than this ad-hoc thing, you could also try to create a new rails "environment" for this use, I guess.