pewc_open_group_inner.php

<?php
/**
 * Add div inside group wrapper
 */
function prefix_open_group_inner( $group_id, $group, $group_index ) {
	echo '<div class="my-group-inner">';
}
add_action( 'pewc_open_group_inner', 'prefix_open_group_inner', 10, 4 );

function prefix_close_group_inner( $group_id, $group, $group_index ) {
	echo '</div><!-- / .my-group-inner -->';
}
add_action( 'pewc_close_group_inner', 'prefix_close_group_inner', 10, 4 );