XP Update Extender allows you to receive updates for Windows XP until 2019. Therefore all it does is to set a registry key pretending to be a version of XP Embedded called â€œPOSReadyâ€œ. It does not modify any system files.
Pretending to be running this particular version of Windows, you will receive updates made for exactly this version of Windows XP.
Those updates may not have been properly tested for your version of Windows XP and might harm your system. Use at your own risk!