title: How to override existing column in Django admin list display?
body: <p>I'm trying to figure out how to override column values in Django admin list display. </p>
  
  <p>My model has field <code>response_bytes</code> which is in <code>list_display</code> in <code>MyModelAdmin</code>. 
  I want admin to show this value in MB or KB etc. </p>
  
  <pre><code>class MyModelAdmin(admin.ModelAdmin):
      list_display = [f.name for f in MyModel._meta.fields] # This contains response_bytes
  
      def response_bytes(self,obj):
          return filesize.size(obj.response_bytes)
  
      def request_bytes(self,obj):
          return filesize.size(obj.request_bytes)
  </code></pre>
  
  <p>Unfortunately it doesn't call methods below. If I created new <code>list_display</code> items with custom names and then rename these methods, it would work. </p>
  
  <p>Can I override existing fields or do I have to define new columns?</p>