@AlanF: Site tagline is controlled by WordPress Core and this falls under plugin territory. So, you can either search for plugin to do it or you can build child theme of Catch Box. For child theme check out http://catchthemes.com/blog/create-child-theme-wordpress/. Then in your child theme, copy function catchbox_header_details() in your child theme functions.php file. For example, the following code, where I have added in <br /> code and text.
/**
* Template for Header Details
*
* @since Catch Box 2.5
*/
function catchbox_header_details() {
// Check to see if the header image has been removed
global $_wp_default_headers;
$header_image = get_header_image();
if ( ! empty( $header_image ) ) :
echo '<div id="hgroup" class="site-details with-logo">';
else :
echo '<div id="hgroup" class="site-details">';
endif; // end check for removed header image ?>
<h1 id="site-title"><a href="<?php echo esc_url( home_url( '/' ) ); ?>" title="<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>" rel="home"><?php bloginfo( 'name' ); ?></a></h1>
<h2 id="site-description"><?php bloginfo( 'description' ); ?><br />Add your new text</h2>
</div><!-- #hgroup -->
<?php
}
.
