from what i understand the cords can fit a 1000 watt or a 400 watt but its up to your ballast to fire it at the proper wattage.. the reason you want a hood upgrade is because you want to distribute the light out evenly and some hoods cant spread a 600watt to its full potential or a 1000, just research the hoods and the ratio of light area.
A ballast is used to control the voltage going to your lamp
1,000 watt ballast will supply 1000 watts and vice versa
hellboy you shouldnt have to change nothing except the bulb and switch it to 400watt...
when pushing 400 watts use the 400watt bulb
when pushing 600 watts use the 600 watt bulb dont Tim the tool man your setup lol