Additional Windchill Capabilities > Manufacturing Process Management > Customizing the Product Structure Explorer (PSE) > Customizing PSE Menus, Toolbars and Popup Menus > Limitations
  
Limitations
Adding new MenuItems to Menus, Toolbar or Popup menus for actions that are not defined is not supported, as PSE currently has no supported API to allow custom actions to be created. Also adding actions to tables for which they are not designed is not supported.