title: VBA excel Overload another add-in function
body: <p>Question!
  I have an add-in we created at work, say foo.xla, and it has a function foo_sub(arg1).</p>
  
  <p>Now, I want to improve the way that foo_sub(arg1) behaves but withour editting the original add-in code, since as soon as they update it, I must migrate my code from the old add-in to the newer. </p>
  
  <p>Is there a way I could write foo_sub(arg1) in a different add-in, say fee.xla, so that every time I call foo_sub from a worksheet the one that get's called is the one I wrote?</p>
  
  <p>Thanks in advance</p>