If Comcast has claimed the devices in their Meraki Dashboard then only they can unclaim them.
You could try creating a Meraki account and seeing if you can claim the devices INTO A NETWORK (not just inventory). You won't be able to claim the devices if Comcast has still claimed them.
If you can claim them, then you can unclaim them, and someone else will be able to use them (they will need to buy licneces to make them work).
https://documentation.meraki.com/Getting_Started_with_Meraki