gistfile1.php

<?php

/**
 * 
 * @package WordPress
 * @subpackage Taxonomy
 *
 * @uses $wpdb
*/

function set_term_taxonomy( $args  ) {
	global $wpdb;
	
	$defaults = array(
		'term_name' => '', 
		'new_taxonomy' => '', 
		'old_taxonomy' => '', 
		'children' => false,
	);
	
	wp_parse_args( $args, $defaults );
	
	extract( $args, EXTR_SKIP );
	
	if( empty( $term_name ) || empty( $new_taxonomy ) || empty( $old_taxonomy ) )  {
		
		return new WP_Error('Required terms not specified', 'required-terms-not-specified');
		
	}
	
	$sql = $wpdb->query( $wpdb->prepare( "UPDATE %s SET taxonomy='%s' WHERE term_id IN (SELECT term_id FROM %s WHERE slug LIKE \%%s\% AND taxonomy == %s)", $wpdb->terms_taxonomy, $new_taxonomy, $wpdb->terms, $old_taxonomy ) ); 
	
	if( true === $children ) {
		
		$children = get_term_children( get_term( $term, $new_taxonomy ) );
		
		foreach( $children as $child ) {
			$wpdb->query( $wpdb->prepare( "UPDATE %s SET taxonomy='%s' WHERE term_id == %s", $wpdb->terms_taxonomy, $newtax, $wpdb->terms, $oldtax ) ); 
		}
	}
	
	return true;
	
}