check text in reply or thread

[Kungfu]

Kind of hard to explain but is it possible to check if something is typed when replying or making a new thread.

basically if i were typing right now and i typed "O3" it would see i typed a number and then it would change the O to something else like ô

Or is it possible to at least put a button, then maybe with ajax it would go through the entire post and check for something like that. Then convert them in the reply box or the new thread box and update it. So as before i typed O3 then i press the convert button and now instead of O3 its a ô.

Thanks in advanced.