Enable root user using the shell command

If you want to switch to root, just use sudo. Typing

sudo su

switches you to the root user after authenticating with your password. This works even if root is disabled in directory utility. Disabling root in directory utility prevents root logins, in particular remote root logins by a malicious 3rd party (to break into your system, a malicious user would need to know your username as well as your password. If root is enabled, half their work is already done).

root access is always available to you through the 'sudo' command.

(Also, disabling/enabling root in directory utility has no effect on programs with the execute bit setuid to root, in case that's why you were asking).