Add/remove ItemNode in PluginDefinition

Is it possible to add/remove ItemNodes in PluginDefinition after initialization phase of plugin? Is there a way to force that the PluginDefinition’s ItemNodes() method gets called again when the plugin is up and running?

Unfortunately no. You can do neither to add/remove ItemNodes in PluginDefinition after initialization phase of plugin nor to force that the PluginDefinition’s ItemNodes() method gets called again.