Sure is, follow these simple steps.
[*]Press Alt + P (or click popups)
[*]Click view and press 4 or go down to nicklist. (Both the same thing..)
[*]At the buttom you should see:
Slap!:/me slaps $$1 around a bit with a large trout
There you change it to whatever, keeping in mind $$1 is the nickname in which you're slapping.
-Andy
