In an earlier article, I tried to argue, somewhat inconvincingly, that theming menu items is less than ideal. I think my example was not well chosen. Fortunately, real life furnished me with a perfect example, during the course of my work.
A client required to associate specific icons with menu items, by specifying a custom class for specific menu items. A legitimate request that has been around for years on desktop menu systems. How to implement this on Drupal? Not so simple using the current menu theming setup.
UPDATE: The comment by jtsnow resolves the general problem of overriding theme functions in a module using
hook_theme_registry_alter(). Woohoo! But the specific problem described below to override the rendering of menu items remains.
I am trying to instruct the menu system to display each item's description underneath the item text, in a smaller font. I located the theme_menu_item() function in menu.inc that currently performs this task.