Test

functions.php

<?php
add_shortcode( 'post_updated_date', 'rv_set_last_updated_date' );
function rv_set_last_updated_date( $atts ) {
	$my_post_meta = get_post_meta($post->ID, 'Update', true);
	if ( genesis_get_custom_field('Update') ) {
		if ( genesis_get_custom_field('Update') == '1' ){
			$last_updated .= 'Aktualisiert am ' . the_modified_date('j. F Y','','',false);
			return $last_updated;
			} else {
				$last_updated .= 'Aktualisiert am '. genesis_get_custom_field('Update');
				return $last_updated;
				}
	} else{
		$published_on = get_the_time('j. F Y',false);
		return $published_on;
	}
}
//* Do those shortcodes when the post has been updated
add_filter( 'genesis_post_info', 'rv_post_info_filter' );
function rv_post_info_filter( $post_info ) {
	$post_info = '[post_updated_date] von [post_author_posts_link] [post_comments before=""]';
	return $post_info;
}