title: change the timezone of datetimeoffset
body: <p>I have a <code>DateTimeOffset</code> variable whose value is 11-11-1989 <strong>16:00:00 +03:30</strong>.
  I can call <code>ToLocalTime()</code> method on it and it shows 11-11-1989 <strong>18:00:00 +05:30</strong>. (I am in India :p)</p>
  
  <p>I am looking for something like this:
  <code>variable1.ToOffset(&lt;timespan&gt;)</code></p>
  
  <p>If I give this function a <code>timespan</code> of 3 hours, It should return me 11-11-1989 <strong>19:00:00 +06:30</strong>.</p>
  
  <p>I tried to change the offset, but offset property is read-only. Does anyone know any workaround for this ?</p>