Hmm, why not just change password and email of the admin account? If nobody knows the passwords and if they can not reset it that is exactly what want, right?
I would not recommend any tweaking of admin account, that might backfire easily in the future.
One a system if you don't use a service it's better to close it. As it's the case with the admin user account I search to see if I can do it without any problem. I also think it's to risky to do but I ask it on the forum in case someone found a way to do it.
And nobody know the password of the admin account ;)