Implementing a Tool script in Godot Engine to update a Label text in an Instantiated scene

export-tool.gd

tool
extends Control

# Set a default value and call the setter and getter functions as needed
# But this txt value IS NOT SAVED in an instantiated scene
export var txt = "Y0" setget set_text, get_text

# But this text value IS SAVED in an instantiated scene
# And it is displayed in the Inspector panel (we don't want that to happen)
export var text: String

func _ready():
	$Label.text = text


# This setter function seems to be called by the Editor before the Label is in the scene producing error messages
# if we don't check that the Label exists
# And I am not sure of the significance of the property_list_changed_notify function call
func set_text(t):
	if Engine.editor_hint and has_node("Label"):
		$Label.text = t
		text = t
		property_list_changed_notify()


func get_text():
	return text