I think there might be a much simpler way to disable the VSP. I'd try it myself, but the VSP sound doesn't really bother me at all. According to the manual, the VSP module only begins making the VSP sound when the Leaf is in Drive AND the brake pedal is released.
So, if one were to simply cut the wire to pin #12, the brake switch input, and tie it to pin #11, switched battery power, the VSP module should think the brake is pressed all the time, so it will never make a sound. Anyone care to try it?