Neat idea, I really like it!
current:
"You may exchange this hero with an OT good non-royal male human warrior in deck or reserve. That hero gains purple brigade, the "king" identifier, and the ability, "Negate Fortress and Neutral Cards."
consider this change:
"Battle: You may exchange this hero and an OT good male warrior from deck or reserve to give the exchanged hero Kingship. (Kingship: character gains Purple Brigade and "King" identifier)"
Having keyword like this, can cut down on txt on cards, because eventually people will know what "Kingship" means, and you can eventually drop the parenthetical explanation.
If they search for a character that is already a royal, not big deal (i mean technically, the anointing prophet should fetch up a David card).
I recommend to take off the "Negate Fortress and Neutral Cards." because 4 abilities on 1 character seem REALLY powerful, and for flavor, the prophet just anointed a new king, they shouldn't have the skill to blow up fortress yet.