title: Replace substring with sed
body: <p>I have a string like this :</p>
  
  <pre><code>test:blabla
  </code></pre>
  
  <p>And with sed, I want to replace what's after the ':' with something else.</p>
  
  <p>I can manage to replace a word, but not the one after the ':'. I searched on the internet for the answer, but I didn't found anything.</p>
  
  <p>Any help ?</p>