I have a script on the menu scene, that gets the value of a variable on my main scene (the Main node is the parent)
if get_node("/root/Main").firsttime == "true":
$Continue.disabled = true
$Continue/ContinueT.bbcode_text = "[color=#646464]Continue[/color]"
I tested the actions and they work just fine, the problem is the condition on the get_node.