I have a menu in joomla that appears on all pages. Some of the items in the menu should be the same on every page, while others need to be dynamically updated based on the page the user is on. I am trying to create an override for the "external url" menu item type (listed under system links), that would allow me to create a menu item parameter the user could populate. Then, I could use this parameter in the menu template to determine what needs to be added to that particular link.
I have been able to add additional parameters to menu items for custom components by editing their xml files. And I know Joomla allows overrides of these files, but I don't think the "external url" menu item is created from an xml file. How could I add an additional parameter to these menu items? Do I need to create some kind of plugin or am I asking for the impossible?