Word replacement per usergroup (adsense related)

[Karabaja]

I'll just quote my post from vb.com since I got an answer that this can't be done without custom modification. I am hoping to have some luck with this here. My original idea was that maybe replacement variable could be applied to certain usergroup, I am not sure if that can be done by some mod or would this need a different approach. In any case I hope someone would find a use for this and make some mod. I am not sure if there is any similar hack that I could maybe check with author if he could add usergroup option for it. Anyway, here is what I was asking about at vb.com:

The problem I am having is that google adsense is misinterpreting one word used often on my board and that results in a lot of ads which are completely off.
The word "keys" which is used on our board in terms of encryption keys, something related to satellite tv. And most of our members are European.
But adsense spiders are relating that word to Florida Keys. And I get a lot of ads are about Florida Keys holidays, resorts, folorida keys fishing etc.

So what I had in mind is to use replacement variable to change "keys" to "ke*s" or something else but only for guests. So that should hopefully help with adsense dropping off topic ads, and it wouldn't cause inconvenience to registered members.
I am not sure if that would cause any other problems, I am assuming that keys isn't used anywhere in the templates or something.
I saw some censorship hacks which I guess could be used, but I didn't find one that has per usergroup option.
Any help would be much appreciated.