Ho there RP, I truly love your work. As such, here's a humble request you could stash in your backlog:
A world where, during the high middle ages, a series of rebellions and revolutions occur across Europe as a result of blooming anti-feudalistic theologies. So not only do you have more successful ATL Cathars and Waldensians, etc., you have other groups taking influence from Gnostic and maybe even Far Eastern churches. As such, a sort of Gnostic revival could be very interesting for you to tackle. Thank you very much for your consideration!
Hmm. I haven't thought about it too far other than Europe, but we maybe see a split between the Catholic Church (centered around Southern Europe/Iberia and maybe more in North Africa), Orthodoxy (about OTL extent but maybe with some Far Eastern touches to it), and this modified Christianity (maybe Northwestern Europe and Germany). If you really wanted to up the ante, you could have this Gnostic faith influence a steppe people who pulls a Timurid on Persia, Sogdia and environs, providing this type of Gnosticism as a rather sizable bulwark against Islam. There would likely be heavier influences on Manichaeanism in the Far East (China would likely be even more of a religious melting pot than OTL).
As for the name, something like "Manimania" could work. I hope to see what you could make out of my suggestion!
Food for though, if Salem went to the God of Darkness first would the God of Light have stopped him reviving Ozma?
Probably. He reprimanded Salem not just for going to the Younger Brother after being turned down but also because she was trying to get them to break the fundamental rules of life and death.