Recovering/Reauthorizing Decommissioned Device on Hosted Mender

Do not think so. The idea of decommissioning is to remove any trace of that device (or actually an authorization set).

Or a setting that would allow a device that was accidentally decommissioned to appear again?

A device which has been decommissioned should always come back in “Pending” state, should it try to connect again.

So the message you are seeing is correct,

Oct 20 03:45:08 ps157 mender[207]: time="2020-10-20T03:45:08Z" level=error msg="authorize failed: transient error: authorization request failed: (request_id: ): authentication request rejected server error message: dev auth: unauthorized" module=state

This should mean that you have an “Pending” authorization set on the server. It can be in two places, either under the “Pending” tab, or it could actually also be under “Devices” tab, as a new authorization set for an existing device. This is typically indicated by a small warning icon on the device.