title: How can I modify (but not replace) icons associated to file extensions?
body: <p>I'm developing a WPF desktop application for windows. It uses its own file type, let's say .foo. This file type represents a file that has been modified by the app. For example, it was originally a .txt but now it is .txt.foo (or maybe I can use .txtfoo).</p>
  
  <p>I'd like to show a small app logo on top of the original icon, similar to what source control systems do (for example showing a small lock on top of the original icon).</p>
  
  <p>I don't want to make completely new icons because I don't want to confuse the user and I'd like them to see the icon they already knew before using the app. So I just want to add the small logo on top of the current icon, whatever it is at the moment. </p>
  
  <p>Is this even possible?</p>