Modify which meta keys are excluded by the SearchWP indexer

gistfile1.php

<?php

function my_searchwp_excluded_custom_fields( $keys ) {
    // by default _wp_page_template is excluded but we want to include that
    // so we'll return everything else we want excluded
    $keys = array(
		'_edit_lock',
		'_edit_last',
		'_wp_old_slug',
	);
	return $keys;
}

add_filter( 'searchwp_excluded_custom_fields', 'my_searchwp_excluded_custom_fields' );