I would say no since good bacteria is aerobic which means it likes oxygen. Bad bacteria is normally anaerobic. If you're not having regular bm's then Oxypowder will definitely help.

Yes, good bacteria will get killed by Oxypowder . The magnesium peroxide will oxidize anything it comes in contact with, and as anyone knows, hydrogen peroxide which works in the same way can be used as a disinfectant. Oxidation does not differentiate between types of bacteria (or your cells for that matter). However magnesium peroxide releases oxygen fairly slowly.