title: Override existing django-admin command
body: <p>In addition to writing custom django-admin commands, <a href="https://docs.djangoproject.com/en/1.9/howto/custom-management-commands/" rel="noreferrer">which is pretty well documented</a>, I would like to be able to override an existing command, like <code>manage.py loaddata (fixture)</code> so I could add some further treatment after that fixtures would have been loaded into my database.</p>
  
  <p>I guess I would have to write a custom command that first calls 'loaddata' and then does its own treatment. Is there a neat way to do things so?</p>
  
  <p>Is there a better solution?</p>