Hi,
Thank you for posting in Microsoft Q&A forum.
1,Yes, we can connect multiple Configuration Manager to a single Intune tenant for Co-management. It's OK to configure devices in SCCM "A" co-management with an intune tennant "B" in your scenario. We can read the following article as a reference.
https://learn.microsoft.com/en-us/mem/configmgr/comanage/overview#configuration-manager
2,To migrate devices to 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.
Here are some good guides to migrate devices to a new tenant for your reference:
Support tip: How to transfer Windows Autopilot devices between tenants
Intune tenant to tenant migration with Autopilot
Tips for migrating Intune managed Windows 10 devices to a new tenant
Tenant to tenant migration strategy (update)
Thanks for your time. Have a nice day!
Best regards,
Simon
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