Yeah, if you don't reinstall, and just make a sound file mod for it, I assume the scripts that control mouth movement would have incorrect file references. The time and hard work it would take to make a proper mod would not make any sense when you can just reinstall. I know how much it sucks, I just had to do it cause I damaged some files trying to mod stuff.
Haha, now you trust me right?
Edit: Yes arnesw sorry, you may be right about the Steam version, as I don't know much about the complications of getting it through Steam. You should try it anyway, could be worth it.