I installed a new horn and it took all of 10 minutes using a screwdriver and a socket wrench. I bought the horn from College Hills Honda via the web. I also watched their video. The fasteners holding the plastic cover over the grill pop out easily with a screwdriver. There is a plastic cover over the hood latch mechanism where the fasteners were no so easy but the horn supplied by College Hills Honda had two extra fasteners included.
When reinstalling the plastic cover, there is a grove that the grill piece fits into so make sure you don't miss this. It looks like it supports the grill.
Now I have a nice deep sounding horn as opposed to the tiny 'beep beep, as before.

 

Just to be clear, you're talking about a GE8 . . . getting to the GD3's horn is a little more involved.