Wow huge thumbs up to the guys who made this possible. This annoyed the hell out of me, and I thought I would just have to live with it.
Following Yamazama's post and the PDF in this thread, I was able to get mine to work exactly the way I want. No horn, no shutoff. Thanks a bunch guys!
A few quick notes that might help out some guys doing this, most have been said in this thread but I missed them going through it and had to go back and re-read.
To enter programming mode, make sure doors and tailgate are closed.
When pressing the programming button for the initial 10 seconds, you also have to be pressing down on the brake pedal.
The LED status light did not illuminate until I had entered the programming mode. I never directly found the LED, but was able to see the glow behind the glove box. If you're having a hard time finding the LED, try entering Bank 1 and scroll through a few options to see if you can see a red glow from the LED. Do your work in an unlit garage to help see the LED if it's not directly visible.
My car horn did not honk when entering the programming mode, bank 1 or 2, and also when scrolling through the options. I was however able to hear what sounded like a relay clicking the same number of times that the horn was supposed to honk. So I would recommend doing the work while it is quiet enough for you to hear just incase your horn doesn't honk.