title: Programatically changing hash of a file without corrupting it
body: <p>Does anyone have any info on changing the hash of a file without corrupting it?</p>
  
  <p>I read about appending a null byte to the end of the file, thus changing the MD5 without corrupting it. Anyone have any info?</p>
  
  <p>The language I wish to do this in is PHP.</p>
  
  <p>Thanks.</p>