Bit more controversial proposal here I bet, since it'd require the in-development Crisis of the Third Century submod/project to play the scenario: reforming the Hellenic faith in WTWSMS could be restricted to Julian the Apostate, unless he was never born or didn't reform it in your campaign in which case it gets opened up to Roman Emperors. In later start dates the reformation failed and Old Hellenism, while still on the decline, has replaced all of Julian's attempted reforms, resulting in the dynamic we currently have, and reformation is remembered as a failed experiment rather than something to try again.