title: Revert AUCTeX version
body: <p>A recent change in how AUCTeX detects modes and indents LaTeX code has made it hard for me to work. I'm currently using version 13.1.2. I'd like to revert to 12.x, or in fact any version of AUCTeX prior to the 13.x series. Is there an easy way to do that?</p>
  <p>I'm running Emacs 27.2 on MacOS.</p>