[Peter Finke]

Jacob, I generally comply with you. Parosphromenus are quite stable and less delicate if kept in a sound and rather stable environment. To my experience, the pH-issue is overstimated if taken as that value itself. Even Parosphromenus do not “need” very low pH, even their eggs do not. There are many reports of successful breeding with a pH around 6.5 (but always below 7!). The thing is not the pH, but the low density of germs and harmful bacteria. The pH, in combination with humid substances, is an important means for regulating that content. The lower the pH, the lower the concentration of germs (as a rule, at least generally speaking).
I cannot tell you generally “safe levels of change” in the aquarium, as you asked for. This is too wide a question. “Create an environment as stable as possible with the least possible concentration of germs”: that would be my recommendation. Not the one or other fix value, with one exception: the water should contain little salts (= a low value of Mikrosiemens/cm). Otherwise the tender eggs and the very young fish of our genus cannot stand the osmotic pressure. Adult fish are more resistant, but they are also adapted to very soft water.