you asked about switching to hps.... I have personally grown plants all the way through with just an MH and just an HPS. my MH still produced wonderful nugs but the hps was a tad bit better, Im assuming it's because HPS bulbs have more lumens than MH bulbs of the same watt. Either way it wouldn't hurt to leave the MH in but you would be giving your plant more lumens with an HPS and that's what it's all about the lumens! they say color spectrums matter, and they do to an extent, but not as much as everyone makes it out to be. It's not like you wont get buds if you don't use a "red spectrum light" it's just people use HPS more because of the "red" but also because of the lumens increase.
In addition I want to add that when growing inside our goal is to mimic the sun which covers all color spectrums not just blue and red. If at all possible which is what i do now is I run my 400wMH and 400hps side by side in my tent. HUGE DIFFERENCE. could be all the extra added lumens could be im giving my plants more spectrum not sure...
just my own personal findings through expirements and research thought I'd share, do with it as you please.