Phew - just got done installing a new replacement horn - WOLO BadBoy *Harbor Freight - $39.95). The sucker is LOUD, and it covers both audio ranges (low and high, unlike the stock smart horn).
The directions for side-skirt removal can be found here:
How To: Side Skirt Removal
The directions for the front panel can be found here:
How To:Front Panel Removal
You don't need to remove the whole front end - just the driver's side. The panel will flex out of the way enough (and to spare) with the passenger side still hooked up.
The stock horn in mounted in front of the steel structural plate, the WOLO horn needs to mount behind the panel. It takes a little jiggling to get it there, but once there, no sweat.
Word of warning - the side-skirt is the toughest part of this mod - I would strongly advise having a second person around when you go to re-install the panel - it takes a bit of flexing, and constant pressure over the side clips, to get it on right. I had to bend like a pretzel to put my left knee, left forearm, etc. on enough of the panel to slide it into place.