I just figured that out as well and it works - yay!
I’m confused, however, why in How to put the config.json generated from Resin Dashboard to the compiled image when build?, a Resin staffer suggested a few months ago that this should work, and why the documentation at https://docs.resin.io/reference/cli/#config-inject-file- also lists ‘resinOS image’ as a supported operand.
That’s the first thing that comes up with Google. It smells like the resin os configure approach is a new thing that isn’t documented anywhere else (e.g. the manufacturing blog post at https://resin.io/blog/advanced-device-provisioning-workflow-for-large-fleets-preloading-and-pre-provisioning/) even though it makes for a much better workflow.