On a regular Hard Drive a secure delete of a file is possible by overwriting it, does simply overwriting the registry key is enough to secure delete the key ?
If not how I can proceed to secure delete my registry key ?
It is very difficult to securely delete something from the registry:
In the forensic wiki, there is an article about the registry structure . You'll find in the bibliography an article about recovering past values which demonstrates that it is extremely difficult to securely delete such registry keys.
So don't store there sensitive data. Or if you have to, encrypt the value.