title: Find and replace every second occurrence of a word in a column macro
body: <p>I want to change every second occurrence of a word in a column to a different word
  example:</p>
  
  <pre><code>Column A    Column B      
  Blank        123
  Blank        124
  XXXXX        125
  Blank        126
  Blank        127
  XXXX         128
  XXXX         129
  XXXX         130
  etc
  Blank        150
  Blank        151
  </code></pre>
  
  <p>I want to change every second 'Blank' to something else e.g. 'Blank1'
  The number of rows varies up to ~ 300.
  There may be up to about 30 occurrences of the 2 'Blank' pairs.
  The XXXX are other labels
  Want end result to be:</p>
  
  <pre><code>Column A    Column B      
      Blank        123
      Blank1        124
      XXXXX        125
      Blank        126
      Blank1        127
      XXXX         128
      XXXX         129
      XXXX         130
      etc
      Blank        150
      Blank1        151`
  </code></pre>