Changing the administrative user on mysql from `root` to something else
Connect to MySQL as -u root, then

First, see what root has:

SHOW GRANTS;


Then add a new user, similar to the root:

GRANT ALL PRIVILEGES ON *.* TO 'foobar'@'localhost' IDENTIFIED BY ('long secure pwd') WITH GRANT OPTION;


where foobar is the "mortal" mentioned in your quote.

Then re-login as foobar to verify it.  Then get rid of root (or at least emasculate it).  Perhaps this

REVOKE ALL *.* FROM root@localhost;


Then verify with

SHOW GRANTS FOR root@localhost;
SELECT user, host FROM mysql.user WHERE user = 'root';


The first should show only GRANT USAGE, which lets root in, but without any privileges.  The second checks to see of root can get in from any other "host".  If there are any ways in, we can discuss zapping them.