Make XML Notepad your default XML editor on Windows 10

First you need to find where xmlnotepad lives on your machine, you can do that by launching it, run Task Manager, click "Details" tab, find xmlnotepad in the list, right click to bring up the Properties and copy the full location text, which is something like this:

C:\Users\Chris\AppData\Local\Apps\2.0\60MPBT3D.ELV\H2QGHQ42.AJQ\xmln..tion_ab3ea86545595e2b_0002.0008_ab38540bc49376db

Then run regedit and open HKEY_CLASSES_ROOT, then "xmlfile" and edit the "shell", "open" "command" so that the default string is:

"C:\Users\Chris\AppData\Local\Apps\2.0\60MPBT3D.ELV\H2QGHQ42.AJQ\xmln..tion_ab3ea86545595e2b_0002.0008_ab38540bc49376db\xmlnotepad.exe" %1

And now "xmlnotepad" shows up in the OpenWith list when you right click and XML file:

and this means you can use this menu to also make it the default, by selecting "Choose another app" and choose:

And check the box "Always use this app to open .xml files".