I have a Genesis 600w HPS bulb and I just ordered a 600w MH bulb that should be here today. I was wondering if turning off my HPS bulb after 3 hours instead of 12, to swap bulbs, would negatively affect/break the bulb?
If I understand your question correctly, it will not hurt your HPS bulb to shut it off and change it after 3 hrs. Of course, just let it cool down a bit before touching/changing it out. Hope this helps.
Definitely let it cool down. I'd give it at least 30 minutes. Just make sure to not touch either bulb with your hands.