I see! I had thought the organization structure was separate from inheritance since in my custom node I specify the node type it's extending (
extends ExistingNode), but then I have to separately place it in the node list using the plugin's class that extends
EditorPlugin. This is done using
add_custom_type("MyNode", "ExistingNode", preload("my_node.gd"), preload("my_node.png")). So even though you need to explicitly set the parent in the node list in when using
add_custom_type, it can only be set to the node it's inheriting from? I would think this would mean that the second parameter should be removed from
add_custom_type then (unless I'm missing something).