An alteration of the Windows registry can be used to make an expired “Windows XP” system resemble a “POSReady 2009” operating system (that is normally used in a highly specialized and restrictive corporate setting).  While this may “work” for many future security updates, making an XP operating system emulate the newer and more modularized POSReady 2009 version puts the end user at risk.  All users should be moving to newer supported operating systems, but it make take some time to transition.  Hardening XP security will be a more reliable choice than tricking the operating system to update as described in articles below. One incompatible update could integrity to be lost so that operating system no longer boots properly.

QUOTE: Microsoft has stopped providing XP users with security updates, forcing them to either upgrade to another, newer operating system, or gamble with their safety. While the latest usage figures show that a large portion of users are moving away from XP, there’s still a sizable number of users who aren’t — or can’t.  If you’re an XP user, or know some XP users, there’s a trick which makes it possible to receive security updates for the aging OS for another five years — right up until April 2019.

The workaround makes use of updates for Windows Embedded Industry (formerly known as Windows Embedded POSReady). This is based on Windows XP Service Pack 3, and the security updates which are being released for it are essentially the same ones Microsoft would have pushed out for XP, if it was still doing so.  You can’t simply install the updates — that would be too easy — and you’ll receive a version mismatch error if you try. But a simple registry tweak is enough to fix that.

More about POSReady 2009 XP in links below

QUOTE: Based on Windows XP Service Pack 3, this version offers more features over Windows Embedded for Point of Service V1 such as Full Localization and XPF Support if .NET Framework 3.5 or higher installed. It is the first version of Windows Embedded that can use the Windows Update Agent to update an installed and deployed image. Mainstream support ended in April 2014 and extended support ends in April 2019