I dont care what the help file says, It wouldn't be the first time the help file is wrong. Do this.

Open mIRC, Disable the Commands.
Go to control panel, Uninstall mIRC.

So that you now have no mIRC installed on your system at all.
Download mIRC. Open it. Behold, the commands are enabled.

The commands are only disabled IF:
* You have mIRC already installed with them disabled. (The installer disregards what you check, and keeps current settings for that item).

On a new system, the commands are enabled. They are not disabled until you have done it manually.

In my test i removed every mIRC folder from my system. I opened Regedit and searched for 'mIRC', I deleted all the relevant keys.