Override datasource URL

what: have an instance of Grafana override one of its datasource URL’s

why: for production evaluation of a “drop in replacement” datasource backend (thanos -> victoria metrics), we set up a second Grafana instance for evaluation using the same MySQL database (alerting disabled), and want to using all existing dashboards as-is with the new datasource backend (which runs parallel to our existing backend). The evaluation will be for an indefinite amount of time. Forking our Grafana database is a nonstarter.

I don’t see a way to do it-- so I need to make local changes to Grafana source?