I like the identifier thing.
But what makes the /noop command so special that you need special behaviour (making it not overridable)? Any script or alias file could override pretty much any other mIRC command, including /set, yet you can trust all of these to work properly because a sane user wouldn't use aliases that will break scripts they use by overriding built in commands.
And it's not worth it going to this much trouble, and sacrificing flexibility and readability, just to make sure it'll work for those users who are not sane. That is a lost cause.