If I was going to DS my 450 I might think about keeping the stock reg/rectifier and running the lights off the AC side. It wouldn't be totally legal here in CA but you could probably get away with it. If a cop stops you (which I doubt would happen)just say "damn battery is dead again!" If I ended up replacing the regulator then I think I'd go full DC. Mixing loads on AC and DC can get a little tricky since many of the handlebar switches share common grounds with several of the functions (like the horn and the ignition kill for example).
That's how I'm setup now and have done 500miles with no problems. I have my headlight, taillight, lic. plate light and brake lt. on the AC side. TS's and horn on the DC. I figured if I needed an emergency light I could turn my flashers on. I do get the head light dimming when I hit the bake at low rpm, but when I get the LED taillight, it should solve that problem.