The XQuery Update Facility has been recently published by the World Wide Web Consortium as a working draft. Among other features, the working draft presents a novel powerful transform expression. A transform expression creates a new modified copy of an XML subtree, where the modifications are specified as update operations. In this paper we investigate the use of transform expressions and provide a method to support transform expressions efficiently: the method avoids copying of the whole modified XML subtree. Our method is based on the idea of shadow mechanism proposed in early work on recovery.