This isn’t very helpful, but what I’d do is create the users in rails rather than via the API. discourse/script/import_scripts/csv_importer.rb at main · discourse/discourse · GitHub could be a start.
But you can go into the container and edit /var/www/discourse/config/discourse.conf and set those variables there and then do an sv restart unicorn (or maybe sv reload unicorn). You’ll probably want to do something like apt-get update; apt-get install -y vim to have an editor.