lighting problems-downgrading Watts

Hi ,I had a 600w MH in my cupboard for a week untill my fuse box packed up and now the light doesnt work,when I looked at the box at says max wattage the flat 250w so that explains that..i think
So firstly
I had about 6 plants but theres only 2 left due to a northern winter and there immature state,I'm thinking of getting a 250w MH bulb and see how that goes ,will that be enough for my 2 remaining plants and could I get away with any more in there?
And secondly
Do I need to change my ballast ?I had one before for my 600w so will that cover everything else below that wattage?
thanks for any help
 
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