Code:
<religion>
<max_witches_per_region uint="1"/>
<max_witches uint="20"/>
<max_heretics_per_region uint="1"/>
<max_heretics uint="80"/>
<max_heretics_conversion_modifier float="1.0"/>
<max_inquisitors_per_region uint="1"/>
<max_inquisitors uint="40"/>
<heretic_conversion_rate_modifier float="0.0075"/>
<heretic_conversion_rate_offset float="0.025"/>
<witch_conversion_rate_modifier float="0.0"/>
<witch_conversion_rate_offset float="0.02"/>
<inquisitor_conversion_rate_modifier float="0.010"/>
<inquisitor_conversion_rate_offset float="0.04"/>
<priest_conversion_rate_modifier float="0.004"/>
<priest_conversion_rate_offset float="0.015"/>
<witch_creation_modifier float="1.0"/>
<heretic_creation_modifier float="0.4"/>
<inquisitor_creation_modifier float="0.3"/>
<min_cardinal_piety uint="4"/> <!-- was 5 -->
<convert_to_heretic_base_modifier float="10.0"/>
<convert_to_heretic_unorthodox_modifier float="0.7"/>
<inquisitor_turn_start uint="120"/> <!-- was 20 -->
<inquisitor_target_crusades bool="false"/>
<founding_conversion_default_rate float="0.0"/> <!-- see britannia for examples -->
<neighbour_normalise_weight float="0.00"/> <!-- see britannia for examples -->
<governor_conversion_rate_offset float="0.00"/> <!-- see britannia for examples -->
<governor_conversion_rate_modifier float="0.000"/> <!-- see britannia for examples -->
<spy_conversion_rate_offset float="0.000"/> <!-- see britannia for examples -->
<spy_conversion_rate_modifier float="0.000"/> <!-- see britannia for examples -->
<owner_conversion_default_rate float="0.00"/> <!-- see britannia for examples -->
<spy_conversion_rate_foreign_modifier float="0.0"/> <!-- see britannia for examples -->
</religion>
At least for the governor, neighbours and the spy it seems to be moddable.