title: Advice on dealing with one-off/special cases in a large code base?
body: <p>Anyone have advice on the best way to deal with one-off or special case business rules in large complex web applications?</p>
  
  <p>Most of the time the requests come in from sales people that promise things to the customer. So as a simple example, lets say someone is selling Stack Overflow. Then a customer that is talking to a sales rep says "I'll buy one subscription but only if you change the background color on the site to black and when sending me emails I would like you to send to one address when emails come to me between 9-5 and use this other address any other time of the day".
  The sales rep says yep no problem sir coming right up. And you wind up with code that is littered with a bunch of </p>
  
  <pre><code>if (customerID == 123) { 
      //do something for this customer
  } 
  </code></pre>