H1000,
Follow the instructions, Step by step to the letter and it won't be an issue.
First, not everyone anyone can follow directions, particularly the first time..
Further, you're asking a guy with no knowledge of DCS, no DCS hardware and no experience using DCS, no understanding of how DCS works or what is a sound file, to learn how to do something he's never done before and is unlikely to have to do again, all to change a horn sound in one engine.
Hence my statement that it would be a "challenge" for him to do so.
Test the file, if it doesn't work, you can always reload the original. MTH will never know if you place the original file back on the engine.
Not necessarily. If things go wrong computer-wise or a TIU-intensive process fails through misadventure, he could, potentially, brick his engine. It's hard to mask that fact. Further, if he is able to attempt to restore the sound file, add that to the list of what he has to do.
I, for one, wouldn't be comfortable recommending to this person that he attempt to use this method to modify his horn sound.
There are lots of things on this forum (and even some in your book) that are not supported by MTH that have become common work-arounds to everyday questions and/or common problems.
"Lots of things" depends upon your definition of "lots". 
Regarding my book, I clearly spell out, generally in bold print, what isn't supported by MTH, sort of like the well-worn "don't try this at home" advice.
For example, in a recent addition to one of my books, using the DCS App on a Kindle, I let people know that it's neither supported nor sanctioned by MTH and that they're proceeding at their own risk. In another example from my books, I also issue strong warnings about opening a DCS Remote and refer people to an authorized MTH tech to do so.
Hacks (it's what this is and its not a dirty word) such as the one that's being proposed are, by their very nature, risky. Those of us who give advice to use "unauthorized" methods to do stuff have a responsibility to spell out the risks as well as the rewards of doing so, while gauging the likelihood of success in specific instances, before responding appropriately.
End of soapbox rant.
