mandala_assimilation_effect

mandala_assimilation_effect = {
	overlord = {		
		send_interface_message = {
			type = event_conversion_good
			title = subject_assimilated_under_your_rule_msg
			left_icon = root
			right_icon = overlord
			show_as_tooltip = { 
				root = {
					if = {
						limit = {
							NOT = { has_government = mandala_government }
						}
						change_government = mandala_government 
					}
					if = {
						limit = {
							NOR = { 
								faith = overlord.faith 
								faith.religious_head ?= root
							}
						}
						set_character_faith = overlord.faith
						set_character_rite = overlord.rite
					}
				}
			}
			if = {
				limit = { has_realm_law = mandala_decree_reverence }
				mandala_converter_piety_effect = yes
			}
		}
	}
	#The Decree
	show_as_tooltip = { change_to_mandala_government_decree_effect = yes }
}

As written in game/common/scripted_effects/tgp_mandala_scripted_effects.txt.