Zigbee2mqtt: getting rid of your proprietary Zigbee bridges (Xiaomi, Hue, TRADFRI)

Hi, I’m planning to upgrade my cc2531 to cc2652.I know I have to re-pair all the devices again. But do I have to remove all the devices in HA first before doing re-pairing? Or we just have to reset the end device and let it re-join?

Also, I know I have to modify the pan_id in the zigbee2mqtt configuration but how do i know what new pan_id should I use?

Thanks in advance