MTH will not do this, and I have repaired one engine were after a period that procedure corrupted a PS-3 Diesel board and it stopped working. $220 part.
MTH Will load a different sound file, but they will not do that type of editing.
Now if for some reason the wrong horn was used for a production engine, they may go back and fix that with the Sound engineer and release an update; but they are not going to do editing with that third party software to just customize what a customer wants. G