migration_set_obedient_vassal_effect

migration_set_obedient_vassal_effect = {
	create_title_and_vassal_change = {
		type = migration
		save_scope_as = change
	}
	every_realm_county = {
		limit = {
			holder = scope:current_vassal
			is_nomad_title = no
			is_noble_family_title = no
		}
		create_character = {
			template = herder_character
			faith = scope:current_vassal.domicile.domicile_faith
			rite = scope:current_vassal.domicile.domicile_rite
			culture = scope:current_vassal.domicile.domicile_culture
			location = scope:current_vassal.primary_title.title_capital_county.title_province
			save_scope_as = herder_character
			after_creation = {
				remove_character_flag = peasant_outfit
				add_to_list = government_change
			}
		}
		change_title_holder = {
			holder = scope:herder_character
			change = scope:change
		}
		title_province = {
			if = {
				limit = {
					has_holding_type = nomad_holding
				}
				set_holding_type = herder_holding
			}
		}
	}
	resolve_title_and_vassal_change = scope:change
	every_held_title = {
		limit = {
			tier >= tier_duchy
		}
		prev = { destroy_title = prev }
	}

	every_in_list = {
		list = government_change
		change_government = herder_government
		remove_from_list = government_change
	}

	scope:actor = {
		add_to_variable_list = {
			name = obedient_vassals
			target = scope:current_vassal
		}
	}
}

As written in game/common/scripted_effects/09_dlc_mpo_scripted_effects.txt.