This allows you to define your own tags for the body of the feedback email. The Array Key should always contain the tag and the Array Value the value. Helpful then replaces the keys with values.

/**
 * Add or replace tags for email body
 *
 * @param array $tags default tags.
 * @return array
 */
function custom_function( $tags ) {
	$tags['{custom}'] = 'My own tag that is replaced in the text.';
	return $tags;
}

add_filter( 'helpful_feedback_email_tags', 'custom_function' );