title: Replace second instance of punctuation in string?
body: <p>Have many strings with the pattern:</p>
  
  <p>A/B/C/D</p>
  
  <p>I just need to change the 2nd '/' to something else (say, *)</p>
  
  <p>So A/B/C/D --> A/B*C/D</p>
  
  <pre><code>gsub('(^[[:punct:]])([[:punct:]])', "*", string) #Didn't Work
  gsub('[[:punct:]]{2}', "*", string) #Didn't work
  </code></pre>