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If you don’t migrate iee, you will have to re-pair all devices. Nothing will work until re-paired,
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No. Only one ZHA instance is supported with a single coordinator, no switching is not supported. It’s a rip the bandaid off and get it done process. Most devices should pick up the existing device names when they re-pair (but no promises).
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If it hasn’t been changed in the past, you should be able to change the Nortek zigbee ieee address after migration using the SI Labs Flasher. In theory you could migrate, and then change the Nortek ieee, and everything should work. But again, no promises and no first hand experience doing this with a Nortek or other ezsp stick. I have done it migrating from a cc2652 stick.
Proceed with caution!.
Changing the SI Labs ieee is a one time only option for ezsp sticks. There is no going back. The “this is permanent” warning in the GUI is not nearly scary enough IMO. You might be thinking “I’ll just test” and end up committing yourself if your not careful.