How to change a scene's exported variable via tool mode?

I have a scene as such:

where the main scene has a show_title variable and before I export the game I run the following plugin:

tool
extends EditorExportPlugin
class_name CustomExportPlugin


func _export_begin(features, is_debug, path, flags):
    # do some checks before exporting
    ...

How do I set the show_title=true within the Main.tscn every time before exporting?

Note: I am using godot version 3.5

Modifying an scene from a tool script

• You load the scene.

  var my_scene := load("res://main.tscn") as PacketScene
  

• You instance it (instantiate in Godot 4).

  var my_instance := my_scene.instance()
  

• You modify the instance:

  my_instance.show_title = true
  

• You package it again:

  my_scene = PackedScene.new()
  scene.pack(my_instance)
  

• And save it:

  ResourceSaver.save(my_scene, "res://main.tscn")
  

Yes, this modifies the project. And no, EditorExportPlugin IN GODOT 3, does not make this any easier.

IN GODOT 4 you can override _begin_customize_scenes to return true, and override _customize_scene to return the modified PackedScene. This way you don't have to save it, and thus the project is not modified.

What I would do

In the script on the root of main.tscn:

func _ready() -> void:
    show_title = true

If you need this set before _ready, you can do it in _init instead.

If that script is not a tool script, that won't happen in the editor. If it is, then you can check if the code is running in the editor with Engine.editor_hint (Engine.is_editor_hint() in Godot 4).

🤷