s it easy to retrieve publish entry for any custom publish type by tag, I've been trying using the following code, nevertheless it just locks me right into a infinte loop.

<aside class="supporting_images">
    <?php /*<?php if($post->ID == 241) : echo apply_filters('the_content', '[slideshow=3]'); endif;  ?>
    <?php the_post_thumbnail(); ?>*/?>

    <?php if($post->ID == 241) : ?>
        <?php
            $query = new WP_Query();
            $query->query('tag=branding');
        ?>
        <?php while ($query->have_posts()) : ?>
            hello
        <?php endwhile; ?>
    <?php endif;?>

Try altering your loop to:

<?php while ($query->have_posts()) : the_post(); ?>
    <?php the_title(); ?>
<?php endwhile; ?>

The have_posts() function just returns true if there's another publish but doesn't increment the loop counter, therefore the loop won't ever finish.