Turn a cloned macOS partition into a unique copy for use with iCloud When copying a bootable partition using the dd command or similar means, the copy runs fine but will use the same IDs as the original. This leads to problems when using Apple cloud services such as iCloud and Messages with both the copy and the original.

I remember seeing instructions on how to change these IDs, I believe by modifying some plist file(s) inside the /System folder, but can't find them any more.

Could someone post the solutition here or point to an existing answer?

Note: Cloning a partition using Disk Utility's Restore operation would avoid this issue.
It appears deleting the files NetworkInterfaces.plist and preferences.plist from /Library/Preferences/SystemConfiguration/, then rebooting, would do the trick - iCloud needs to be set up from scratch again.

But that's a bit of an overkill, as it removes some other valid configurations (network setup, VPN connections etc.) as well.