Hi Jaro,
Hope everything is going well.
==>Do the machines enrolled through the old co-management have to be removed from intune to be included again through the new co-management?
1, May we know if you are still using the same Intune tenant? If yes, theoretically you don't need to remove these machines from Intune to join the new co-management. When these client machines receive co-management policy, they will detect that they have already enrolled in the target Intune tenant.
2,If you are using a new Intune tenant, you'll basically need to un-enroll the device from the old tenant and re-enroll them in the new tenant to join the new co-management.
Here are some good guides to migrate devices to a new tenant for your reference:
Tips for migrating Intune managed Windows 10 devices to a new tenant
Tenant to tenant migration strategy (update)
Note: The non-Microsoft links are just for your reference.
Thanks for your time. Have a nice day!
Best regards,
Simon
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