After you swap out to LED park lights if you want to reduce the headlight load you can wire up some relays to switch them to series load instead of parallel. That will make them dimmer but not really dark. It will cut the load in half though
The other thing would be using some relays to switch them out you can add several silicon diodes in line. You get a .7V drop across a diode so add 5 of them in series will drop you 3.5V. Just make sure to pick big enough diodes to handle the load.