1-Never heard of any law or fine imposed on HID light, or its not implementing.
2-If your horn wiring is all ok then you have to upgrade your battery or higher mAh, HID uses more current then LED. To check just turn off HID and check the horn sound if its ok then battery need upgrading.
I just suggest you to check chines LED light result before buying battery, because it cheaper then battery and result is better then HID (with 6 leds light as mentioned in post).