I looked around in the export_descr_character_traits.txt and noticed:

Code:
Trait IAmPope
    Characters family
    Hidden

    Level Character_Is_Pope
        Description Character_Is_Pope_desc
        EffectsDescription Character_Is_Pope_effects_desc
        Threshold  1 

        Effect Level  1
and

Code:
Trigger factionleader_pope
    WhenToTest BecomesFactionLeader

    Condition FactionType papal_states

    Affects IAmPope  1  Chance  100
I used give_trait 'character' IAmPope and nothing happened except the priest became a bishop...