Override/Extends a plugin

plugin_extends.php

<?php
/**
 * Plugin Name: Extend a plugin
 * Version: 0.0.1
 * Author: Jonathan Bardo
 * License: GPLv2+
 * Author URI: http://jonathanbardo.com
 */

if ( ! class_exists( 'Date_Range_Filter' ) ) {

	require plugin_dir_path( __FILE__ ) . '../date-range-filter/date-range-filter.php';

}
 
class Test extends Date_Range_Filter {
  
  public static function setup() {
    parent::setup(); // optionnal
  }
  
  public static function OVERRIDE_PARENT_FUNCTION() {
    // Isn't that beautiful?
  }
  
}

remove_action( 'plugins_loaded', array( 'Date_Range_Filter', 'setup' ) );
add_action( 'plugins_loaded', array( 'Test', 'setup' ), 20 );