Hello,
I’m struggling with low signal issues and some connectivity problems using ZHA, while reading seems Z2M appears to handle better the signal and devices as well of having a better map to understand the devices connections.
Is there some guide / road to follow in order to migrate ZHA → Z2M ?
I would like to avoid the scenario open all boxes, move furnitures etc… to re-pair everything 
No but here is a somewhat related discussion → https://github.com/Koenkk/zigbee2mqtt/discussions/16478
Regardless, low signal issues and connectivity problem should be no different if using the same Zigbee Coordinator and the same Zigbee router devices, so be sure to read and and try to follow → https://community.home-assistant.io/t/guide-for-zigbee-interference-avoidance-and-network-range-coverage-optimization/515752
I agree that ZHA or Z2M should not make a difference regarding link quality.
That being said, my understanding is that pairing happens between devices and the coordinator, so moving from ZHA to Z2M shouldn’t impose re-pairing.
got it!
Also in my thoughts I had the same view regarding signal, but some post people claim some issues of pairing, devices reconection and better signal handling did improve moving to Z2M.
I will try to arrange the Conbee in a different place to see if connection improves
I think that you would see a much bigger difference if you follow → Guide for Zigbee interference avoidance and network range/coverage optimization.
As mentioned there also maybe consider buying a CC2652P based Zigbee Coordinator with external antenna, like example the “Sonoff ZBDongle-P”, see → https://community.home-assistant.io/t/iteads-sonoff-zigbee-3-0-usb-dongle-plus-model-zbdongle-p-based-on-texas-instruments-cc2652p-20dbm-radio-soc-mcu/340705
I do not believe that Zigbee2MQTT has a build-in feature/function to keep an already formed Zigbee network that existng Zigbee Coordinator?
If not then you would at the very least have to manually enter the Network Key and PAN ID that you where using before into the Zigbee2MQTT configuration.
That would be reverse of steps here → https://skyconnect.home-assistant.io/migrate-zigbee-zha/
For reference also suggest reading this too → https://skyconnect.home-assistant.io/migrate-conbee/
I don’t use Z2M, but I know you can do backup/restore from ZHA, so I thought there was some interoperability involved 
Unfortunately not at the application-level, however, the Zigbee Coordinator firmware does have a key store and stores all joined devices, so if you enter the Network Key and PAN ID in then you at least do not have to manually re-repair all of your devices as they are already approved by the Zigbee Coordinator as they will at least try to reconnect, but at the application-level you will still be like adding them from scratch, so you need to setup all your devices and device settings for each device again.
ZHA to ZHA migration is possible → https://skyconnect.home-assistant.io/migrate-zigbee-zha-only/
The problems are when want to migrate from ZHA to Zigbee2MQTT, or from Zigbee2MQTT to ZHA.
You will not get a seamless migration as all of the metadata is stored in host application databases.
Cross-applications migration only saves you the trouble of having to manually re-pair all devices, though note that you will still probably have to re-pair some devices, as well as re-do all application-level stuff.
This disclaimer below is posted on both these two guides:
“Note: this procedure only helps migrate basic network settings to your Home Assistant SkyConnect, customizations like device names will be lost and automations will need to be updated. Most powered devices like lightbulbs will be re-discovered over time (you can speed this up by rebooting the device) but your battery-powered devices may need to be re-joined to the network for the migration to complete. There is currently no migration path to migrate all settings and devices.”