[ClassiPress theme + Anonymous plugin] Change the anonymous author name to the one from custom field

functions.php

<?php

/**
 * Change the anonymous author name.
 *
 * @param string $author_meta The value of the metadata.
 * @param int    $user_id     The user ID.
 *
 * @return string
 */
function childtheme_modify_anonymous_author_name( $author_meta, $user_id ) {
	global $authordata, $post;

	if ( ! is_singular( APP_POST_TYPE ) ) {
		return $author_meta;
	}

	if ( ! $user_id ) {
		$user_id = isset( $authordata->ID ) ? $authordata->ID : 0;
	}

	$user = get_userdata( $user_id );

	if ( 'anonymous' != $user->user_login ) {
		return $author_meta;
	}

	// get user name from custom field (REPLACE THE FIELD NAME!!)
	$custom_user_name_field = get_post_meta( $post->ID, 'cp_anonymous_custom_name', true );

	if ( ! empty( $custom_user_name_field ) ) {
		$author_meta = $custom_user_name_field;
	}

	return $author_meta;
}
add_filter( 'the_author_display_name', 'childtheme_modify_anonymous_author_name', 10, 2 );