OK, hold that, based on @ScruffR post https://community.particle.io/t/where-can-i-find-the-device-claim-code/20011/2 I worked through the API calls required.
Wow, you can do a lot via the API …
For reference:
# Claim an online device
curl -d access_token=<access token> -d id=<device id> https://api.particle.io/v1/devices/
# Unclaim a device
curl -d access_token=<access_token> -X DELETE https://api.particle.io/v1/devices/<device id>
# With access token taken from settings tab in https://build.particle.io
# and device ID from particle serial identify