title: Quickest way to modify md5 hash value of a zip file
body: <p>I have around 500 zip files that i have to place in a directory for a process to process them. </p>
  
  <p>The process calculates the md5 hash value of the file before processing it. If the hash value of the file is the same as one it is aware of (stored in a database) it ignores the zip file and continues to the next one. </p>
  
  <p>Each zip file contains two files:</p>
  
  <ul>
  <li>An excel document</li>
  <li>An XML file with some metadata about the excel document</li>
  </ul>
  
  <p>As part of testing, i need to process all zip files several times. Currently, to allow the process to not ignore them, i just clear the hash values from the database before i run my tests. </p>
  
  <p>Is there a way i can run the tests without having to clear the recorded hash values? I tried renaming the zip files but that does not seem to change the hash value. </p>
  
  <p>Is there a quick way to make a change to the files in the zip files so that the hash value changes every time (using any tool in Unix or Windows)?</p>
  
  <p>As an example, if i extract all the files (each pair in its own folder), is there a way i can make a small change to the xml and re-zip the files (assuming it is going to be more tricky to update the excel document)?</p>
  
  <p>Thanks</p>