override_flatsome_code.php

function overwrite_shortcode() {

    function overridden_ux_accordion_item( $atts, $content = null ) {
	extract(shortcode_atts(array(
		'title' => 'Accordion Panel',
		'class' => '',
	), $atts));
	$classes                 = array( 'accordion-item' );
	if ( $class ) $classes[] = $class;
	return '<div class="' . implode( ' ', $classes ) . '"><a href="#" class="accordion-title plain"><button class="toggle"><i class="icon-angle-down"></i></button><h2>' . $title . '<h2></a><div class="accordion-inner">' . do_shortcode( $content ) . '</div></div>';
    }

    remove_shortcode('accordion-item');
    add_shortcode('accordion-item', 'overridden_ux_accordion_item');
}

add_action('wp_loaded', 'overwrite_shortcode');