Forums Scripts & Popups sending spoofed text

I'm not sure if this is doable, it seems like some clever trickery could make it happen, but I can't put my finger on it. maybe some sort of use of a null echo or something.. im not sure.

Is it possible, for instance, to type a letter "a", and have it appear to you that what you sent was the letter "a" to the chat window, but in fact what was actually sent to the chat was the letter "b" ?

using

on *:input:*:{
set %f $replace($1-,a,b)
say %f | halt
}

will swap "a" to "b" just fine, but the chat window shows "b" as well, is it possible for it to show "a" only to you?

just to absolutely clarify: you type "a", you see "a", everyone else on irc sees "b".