title: Modify all the values in the column of a Pandas Series
body: <p>I have a column with 9-char long numbers. I need to perform some operations on all values in that column to reach a length of 12. Here is the original data:</p>
  
  <pre><code>493    123456789
  494    123456789
  496    115098765
  497    123456789
  498    987654321
  499    987654321
  </code></pre>
  
  <p>Now, I need to perform some modifications to the numbers:</p>
  
  <ul>
  <li>after the first 1, need to insert 20</li>
  <li>before the last 5 numbers, need to insert a 0</li>
  </ul>
  
  <p>The desired solution is:</p>
  
  <pre><code>493    120234056789
  494    120234056789
  496    120150098765
  497    120234056789
  498    920876054321
  499    920876054321
  </code></pre>
  
  <p>How can I do that? 
  Thanks in advance.</p>