Excellent wee plugin.
Just edit the /wp-content/plugins/dirtysuds-kill-howdy/greetings.txt file with your message(s) and there's a new welcome every day that doesn't make your users want to punch the computer. This is important for your credibility.
Don't worry about the %1$s in the default greetings.txt file, the plugin will deal with that. It's just a placeholder for the user's display name. My greetings.txt file contains:
Nothing else. I might put "Merry Christmas," in there if I remember.
Good work. Helped me figure out a bit more about how plugins work, too.