As per this MSDN link,
There is no way to replace only part of the visual tree of a control; to change the visual tree of a control you must se
Long story short, this seems to be the link nowadays:
https://docs.microsoft.com/en-us/dotnet/framework/wpf/controls/button-styles-and-templates
(I copied the template for button from that page, and it does indeed seem to be the one.)