title: Modify Returns of existing Setup
body: <p>Let's say I have a standard setup that looks something like this:</p>
  
  <p><code>mock.Setup(myObj =&gt; myObj.MyMethod(It.Is&lt;MyT&gt;(item =&gt; IsTrue(item)))).Returns(someList)</code></p>
  
  <p>Is it possible in a separate line of code to identify the exact same <code>Setup</code> (mocking the same method with the same <code>It.Is</code> criteria), and then modify the <code>Returns</code>?  For example, suppose under one condition I want <code>MyMethod</code> to return the list {0,1,2} and then later I determine that under the same condition I also want to return {3,4,5}.  Because of the way the code is structured, I don't know about the {3,4,5} a priori so I cannot use it with the initial setup.</p>