event_change_movement_power_effect

event_change_movement_power_effect = {
	if = {
		limit = {
			$VALUE$ >= 0
		}
		if = {
			limit = {
				exists = var:movement_power_increased_event
			}
			set_variable = {
				name = movement_power_increased_event
				value = {
					value = var:movement_power_increased_event
					add = $VALUE$
				}
			}
		}
		else = {
			set_variable = {
				name = movement_power_increased_event
				value = $VALUE$
			}
		}

	}
	else = {
		if = {
			limit = {
				exists = var:movement_power_decreased_event
			}
			set_variable = {
				name = movement_power_decreased_event
				value = {
					value = var:movement_power_decreased_event
					add = $VALUE$
				}
			}
		}
		else = {
			set_variable = {
				name = movement_power_decreased_event
				value = $VALUE$
			}
		}
	}
	#force the update of variables to immediately show changes
	if = { #for characters
		limit = {
			exists = var:movement_power_individual
		}
		update_character_movement_power_effect = yes
		top_participant_group:dynastic_cycle ?= {
			update_movement_power_effect = yes
		}
	}
	else = { #for movements
		update_movement_power_effect = yes
	}
}

As written in game/common/scripted_effects/10_dlc_tgp_scripted_effects.txt.