Convert an Addon Domain to its Own Cpanel Account Separately- WHM Tutorials
Managing Multiple Domains as Addon Domains into One cPanel Account ?
Now you can Separate any Addon Domain to its own cPanel Account Separately using WHM.
This solves Multiple Purpose at the same time. If you want to deliver the Client - its own cPanel Separately, then in that case. You can convert his addon domain to its own cpanel.
Let me know if there are any questions.