Using hook_theme_registry_alter()
I think you are trying to alter a $theme_registry['aml']['function'] which doesn't exist.

Try have a look through the $theme_registry array, and find what you want to override, put this in where you currently have "['aml']". I am guessing you want "['menu_item_link']", but you will have to check. 

Then change theme_menu_item_link to aml_menu_item_link.