All you have to do is quote the person above and change their message! =) Make it hilarious, stupid, creative, whatever you want. If you want to your messages to be changed because you think it's fun, quote the person you want to change your message and put Quote Me!
And for goodness sake, don't put any bad words, sex-relating things, disturbing pics, etc. when you change their message; if you do, I'll have to downgrade your rep.
Have fun!