title: Replacing a character with another - always the 3rd last character postion from the right - how to do that?
body: <p>I have an invoice number.
  I would like to replace the 3rd last character with a dot (.)</p>
  <p>Example:</p>
  <pre><code>XA260153758i01
  </code></pre>
  <p>I would like to replace the small <code>i</code> with dot (.):</p>
  <pre><code>XA260153758.01
  </code></pre>
  <p>Now, the small <code>i</code> could be anything, So I do not know what character will be in the 3rd last postion, I only know that the 3rd last character should always be replaced with a dot (.)</p>
  <p>How to script that ?</p>