i went from dual 175watt venture bulbs to dual 400watt radiums/pfo400hqi a few years ago. which is a greater jump than your going through....but same idea...
i just reduced the exposure time the corals had to the 400watters at a time....my reasoning was that in the beginning of summer, some of us(not me:D) get sunburnt from the first couple outdoor activities envolving being out in the sun....so u could put on sunscreen, or u could just be smart about your exposure and ramp up the hrs/day and just develop a nice tan:D
so back to the tank, i started this on the weekend (u could just set your timer up to trigger twice a day)and started out doing 2hrs of MH on twice a day. then ramped up a 1/2 hr per day or two.....i had no noticeable bleaching or lightening of coral....i actually hurried through this process and did it in 3-4 days.......HTH