title: How to change year value in numpy datetime64?
body: <p>I have a pandas DataFrame with <code>dtype=numpy.datetime64</code>
  In the data I want to change</p>
  
  <pre><code>'2011-11-14T00:00:00.000000000'
  </code></pre>
  
  <p>to:</p>
  
  <pre><code>'2010-11-14T00:00:00.000000000'
  </code></pre>
  
  <p>or other year. Timedelta is not known, only year number to assign.
  this displays year in int</p>
  
  <pre><code>Dates_profit.iloc[50][stock].astype('datetime64[Y]').astype(int)+1970
  </code></pre>
  
  <p>but can't assign value.
  Anyone know how to assign year to <code>numpy.datetime64</code>?</p>