Can I use Destroy utility to completely remove the Key on the user's machine like the Key Inspector tool?

The Destroy, Remake utilities and functions are used with the protected app on the user's machine. They actually do not remove the Key completely due to security reasons. In addition, the Destroy will not destroy the trial license (i.e. the Key in the Evaluation/Not Registered mode), or the license that is already expired. The Destroy and Remake do the same thing to reset the Key, except that the Destroy will give a Destroy-Code for verification.
Here is how you can completely remove the Key on the user's machine, without using the Key Inspector - intended for use during development. Run Register.exe (either Local or Network Key version of the Key type). A Registration ID is provided. You then enter it into LicenseKey Manager, select the Destruction implementation, and generate the License Key. When you enter this License Key to Register.exe, it will remove the Key completely.