Is it possible to replace a function within a PHP class?
It sounds like what you want to do is extend the class, and override that particular function.
Class Your_Tribe_Image_Widget extends Tribe_Image_Widget{ function example_function() { // Call the base class functionality // If necessary... parent::example_function(); // Do something else useful }}
You could probably have an include_once to the target plugin at the top of your file and then extend the class of the target plugin instead of the WP_Widget class:
include_once otherPlugin.phpclass My_Awesome_Plugin_Overloaded extends Someone_Elses_Awesome_Plugin{ function example_function(){ return 'woot'; }}