The question I have is not about the 400s but the Actinics you added. How much additional wattage did those add, and what about that photoperiod? You probably still have more light than you did originally, because of the additional actinics, so you shouldn't have to acclimate down for as long. Or, you can acclimate back down by varying the photo periods of all of your additional lighting and cutting back on the MH.

Personally, I think if you do it like you have thought, and as Ace recommended, you will lessen the chance of browning out.