It will only make things better. Just make sure that you keep it far enough away from the canopy if it's 250 watts or more. That's the only thing that could hurt by making the switch is the heat. I'm using a 150w and the leaves are almost touching the light and it's all good. Check my journal out. Give your girls a gift this holiday. Brighten their lives up with a nice HPS.
I believe it's...
8 inches away - 250watt
16/18 inches away - 400watt
24 inches - 600 and up.
Ventilate, ventilate, ventilate.