I just build an own Version of ResinOS with bitbake and just tried some funny things like RESIN_CONNECTABLE = 0 and just using an ssh docker container as base image. Then added a config.json with wifi settings.
Unfortunately the device is not connecting to the network, and when I just plugges keyboard and monitor to my raspberrypi zero it only shows the resin splash…
Is there a way to access the console with a keyboard??
Have you tried setting the DEVELOPMENT_IMAGE var to 0 as well? It looks like your use case fits the development image variant which should also allow passwordless root access through the console.