override-flatsome-shortcode.php

<?php

function my_shortcode_function_from_main_theme(){

  return "okey";
}

//add a custom shortcode 

add_action( 'init', 'my_add_shortcodes' );

function my_add_shortcodes() 

{  remove_shortcode( 'divider' );   
   add_shortcode( 'divider', 'my_shortcode_function_from_main_theme' );}