User blog comment:LurkerLordB/Survival of the Cathars/@comment-1593341-20111120023830

You could look at the Albigensian Crusade as a POD. Specifically the murder of the Papal legate that caused the crusade. This could allow Catharism to further spread and gain more support from Aragon and possibly Armagnac causing the crusade to fail and Catharism to entrench itself in the area. I don't know if it would ever see widespread acceptance or remain regional but its a start. The failure of the Albigensian Crusade would also greatly affect the political makeup of the region. Marcpasquin has a timeline like that here