This would be a nice feature (it's been suggested before, usually to allow 'encryption' scripts to modify an on *:text as it comes in so other scripts can play with the 'real' text too), or on a larger scale as a /parse command (which wouldn't *modify* the information coming from the irc server but instead allow the user/script to 'fake' messages coming from the server). Khaled has said he has no intention to add /parse as it could lead to some major desyncs between client and server.
I like your suggestion because it could perhaps be applied to certain events only, and would hopefully not be allowed to confuse mIRC (and ultimately the user) to such an extent a /parse command could.
A 'scripted' solution to this is to create a 'middle-man' with sockets and hide/modify/resend information from there.
