Thanks, Matt. I should read the instructions more carefully before I request new functions. I just thought the moderation was about words, not IP-numbers.
As to the advisability of blocking IPs. It is true that one category of trolls are adept at circumventing troll control systems, and in this category you find spammers and such. However, there's a category of trolls that are common users too.
The user I've reacted to is plain obnoxious; going OT at once and going ad hominem against other commenters or me for being idiots and such. I doubt this person is as versed in the ins and outs of the internet. For them, a troll control function would be advisable.
And apparently there was one all along. So again, thanks. :)