Just replace the circuit breaker and screw in new bulbs!
Lights are on separate circuits that the outlets. They are typically on a breaker that is 1 amp for each light bulb plugged into the loop. My 1,300 square foot house has 2 x 15 amp breakers for the lights. If I were to go outside, place a rectifier between the circuit breaker and the breaker box, my lighting circuits could be converted to 12 volts in less than 10 minutes. All that would be left would be screwing in the 12 volt bulbs.
Better than a 12 volt system would be a 4.5 volt led lighting system. They don't waste energy on heat. Simple stuff. Quick to do.