This inspector plugin provides way to set property of NodePath type under ItemMenu (VBoxContainer) node. Children must be instance of Button. This plugin helps to choose siblings of the button in focus entries.
CustomNodeSelector.gd: Specifies handled objects and property type.
NodeSelector.gd: Set property value and execute dialog to choose one of the siblings.
Selector.gd: Sibling chooser in list.
See official document of the inspector plugin for more detail.