Not able to override plugin’s default css rules

Question

If you want to do it this way, it has to look like the following:

add_filter('style_loader_src', 'wpse127340_replace_stylesheet', 10, 2);
function wpse127340_replace_stylesheet($src, $handle){

    if ('your-plugin-script-handle' == $handle)
         return get_template_directory_uri().'/css/themes-copy-of-plugin.css';

    return $src;
}

Replace your-plugin-script-handle and themes-copy-of-plugin.css with what you want it to be.