Shoutbox

Not hook richedit really...these are windowless controls, not richedit (specifically the WLEditT class)...meaning that you have to call the functions to change them (which are in messenger, but it is possible to compile a header for them in c++, among other ways).

You can use active accessibility too.

Once you have that, you can modify it, like plus does...however adding text may not be possible, or plus would probably let scripts return a string longer than the message in the Message Received event..