How to make exportable variables apply visually in the editor?

For some (most?) of those functions you can disable on _ready

func _ready() -> void:
    var in_game: bool = not Engine.is_editor_hint()
    set_process(in_game)
    set_process_unhandled_input(in_game)
    set_physics_process(in_game)

    if not in_game:
        return
    # normal ready etc...

I get that though, it certainly adds complexity so tools scripts aught to be worth it.

This plugin “Hoist” might help, I’ve kept my eye on it, but I usually benefit enough from making tool scripts or dive into making plugins instead.