functions.php

<?php

/**
 * Alternate Title for Subpages
 *
 * @author Bill Erickson
 * @link https://gist.github.com/billerickson/eae1345d8df6c45c47aa
 *
 * @param string $title
 * @param object $subpage
 * @return string $title
 */
function be_subpages_alternate_title( $title, $subpage ) {
	$alt = esc_attr( get_post_meta( $subpage->ID, 'be_alt_link_title', true ) );
	if( $alt )
		$title = $alt;
		
	return $title;
}
add_filter( 'be_subpages_page_title', 'be_subpages_alternate_title', 10, 2 );