To use Autopilot, it is important to register a Device ID first. New Windows Device devices can be automatically or manually registered as Auto-Pilot devices through OEMs, resellers, partners and IT help-desks, but the more to consider is probably the Auto-Pilot scenario for existing devices.
The most important prerequisite to get the Device ID is that these Windows devices must be Intune enrolled. Then, when creating the Auto-Pilot profile, if the "Convert all targeted devices to Autopilot" option is set to 'Yes' and these computer accounts are assigned, Device IDs will be collected and registered in the Auto-Pilot device list. This is explained in the following link.
Automatic registration of existing devices - Windows Autopilot | Microsoft Docs
If we look at how it actually works in more detail.....
First, the AAD Join device works fine. Device ID values are collected, registered in the Auto-Pilot device list, and profile assignment is automatically performed. The device name icon is displayed as pink in the Azure AD Device list.
If it is reinstalled in the OOBE environment, the existing device name is automatically changed to Auto-Pilot's Device Naming Rule in Azure AD Device and MEM Intune lists.
Second, the Hybrid AAD Join device does not support transforming, it is also mentioned in the link above.
So it doesn't work? Actually the device status is not changed like an AAD Join device, but a new device list is created with the Device ID value of the Hybrid AAD Join device. The two devices in the figure below are actually the same machine.
Also, it is registered in the Auto-Pilot list. However, it is only registered and is not automatically assigned to Auto-Pilot profile like AAD Join device.
If you ignore this and manually reassign the Auto-Pilot profile and reinstall the machine in the OOBE environment, normal installation is possible with the company's Auto-Pilot environment.
And when the installation through Auto-Pilot is completed, the device name that was shown as the Device ID value in AAD Device lists is also changed to the value according to the Device Naming Rule specified. Also, it is confirmed that a new device has been registered with this device name in the MEM device list.
If the company no longer does AD Join and decides AAD Join based on device management, wouldn't this scenario also be usable? It's my personal opinion. Of course, the administrator has to remove garbage device information (previously device name, TEMP-HAAD in the picture above) from the AAD Device and MEM device lists if it needs.
Third, if AAD Registration devices need to be installed with Auto-Pilot next time... These devices are Intune registered and assigned, but nothing has changed. However, if you change the ‘Device ownership’ of this device to "Corporate" in the MEM portal, it will change to an Auto-pilot device.
Then, if this device is completed to reinstall Windows via the Corporate Auto-Pilot in OOBE., automatic change of device information in AAD Device or MEM portal is completed as cleanly as AAD Join device.
