Military: War
The anger, fear, and sense of betrayal many felt over the abandonment of the Antecean pantheon did not go away with the official edict. Especially amongst those that had been assimilated into Antecean culture, the condemnation of their spiritual beliefs was a potent slap to the face. The next several years saw much in the way of dissent and pushback. It wasn't until 5 years after the proclamation that the disparate, dissenting voices began to organize.
Antecean leadership responded in force, but the newly formed conglomerate of "spiritual warriors" would not be cowed so easily. By 910 AI, the conflict escalated to a full-scale civil/holy war. Ultimately, the continent-spanning empire won the day, though restrictions on private worship were relaxed as a minor concession to convince some of the rebels to peacefully lay down there arms. This never stopped the private-sector stigma against those that practiced the old ways, of course.