I’m a bit ashamed about the above post. But I’ll leave it here for posterity.
The mistake was mine. Override files can only override .service files that define how the service is brought up, etc. you can’t put any other options in there. The place to make the edits was inside the /etc/systemd/resolved.conf which – works.
Another question, which doesn’t belong here, is how to get all these services to work together, networkmanager and dns pulled from dhcp with resolved / with vpn…