I just accidentally found out that skype allows you to edit past messages using a regex (or at least a perl like edit syntax ..)

i just wanted to fix a past message like i always do.. and entered:
s/m/r/

and wondered why it wasn't sent.. when i discovered that it actually fixed the above message :) (luckily.. i didn't use much m's in that line)

you can even find that feature mentioned on the web.. although no idea if there is an official documentation ?