Use Font-Awesome 4 icons in theme but keep FA5?

Ah, sorry, can you restate what I did wrong now?

  • I have an SVG file in the assets folder named old.svg
  • I reference it in about.json like this: "icons-sprite": "/assets/old.svg"
  • In common/head_tag.html, I have the following code:
<script type="text/discourse-plugin" version="0.8">
    api.replaceIcon('shield-alt', 'icons-sprite');
    
</script>

But something’s wrong with what I did. Sorry for the annoyance I caused you, but I kind of want to finish this quickly.