1) If not already updated, download and install Microsoft's updated Windows Installer 4.5 (KB942288-v3) from
https://download.microsoft.com/download/2/6/1/261fca42-22c0-4f91-9451-0e0f2e08356d/WindowsXP-KB942288-v3-x86.exe

2) Set a System Restore point marked, say, "Spoof POSReady ID registry edit"

3) Put the following POSReady spoof t?ext (omit the hyphen lines) in POSReady.txt, rename to POSReady.reg, right-click Merge, Yes.
----------
Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\WPA\PosReady]
"Installed"=dword:00000001
                                                                                [<-- BLANK LINE]
                                                                                [<-- BLANK LINE]
----------

4) Navigate to:

https://www.catalog.update.microsoft.com/search.aspx?q=kb4019276

5) Find down to POSReady, Windows XP Embedded versions of KB4019276

Click Download button for that version. Click English in the opening language window (or other language).

6) Navigate to:

https://www.catalog.update.microsoft.com/search.aspx?q=KB4230450
 
7) Find down to POSReady, Windows XP Embedded versions of KB4230450:

Click Download button for that version. Click English in the opening language window (or other language).

8) For each KB file: click, accept install, reboot.  (Both create restore points just in case.)

9A) Now edit the following registry entries to read as shown:
(These may be automatic merge .reg texts, but to be careful, I entered them manually.  If you aren't sure how, look up Regedit 5 editing instructions.)

9B) After navigating the chain of registry keys, click the key TLS1.1, in the right panel, right-click "OSVersion", click Modify, enter the Value data shown above, click OK.  (I had to change "3.6.1.0.0" to "3.5.1.0.0" shown in obvious German in the source.)
----------
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\AdvancedOptions\CRYPTO\TLS1.1]
"OSVersion"="3.5.1.0.0"
----------

9C) Next click the key TLS1.2, in the right panel, right-click "OSVersion", click Modify, enter the Value data shown above, click OK.  (Likewise I had to change "3.6.1.0.0" to "3.5.1.0.0")
----------
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\AdvancedOptions\CRYPTO\TLS1.2]
"OSVersion"="3.5.1.0.0"
----------

10) Open IE8, click Tools, Internet Options, Advanced tab, pull the thumb bar all the way down.  You should see new checkbox options for "Use TLS 1.1", "Use TLS 1.2". (KB4230450 will install these checkboxes, but they won't work without KB4019276.)

11) Uncheck "Use TLS 1.0" (insecure). Leave unchecked "Use TLS 1.1" (already obsolete).  Check "Use TLS 1.2".  Click OK.