How to replace a link in the header?

[linlinxza]

I am trying to replace the domain, i.ytimg.com in the header with inv.nadeko.net here:

<section class="rssguard-mhead">
    <div style="float: right; margin: 10px;"><!-- Should it remain here??? --></div>
    <span class="msmall">Written by James Julier Art Tutorials</span>
    <h1><span class="mlinks">&#32;&#47;&nbsp;<a class="menc" href="https://i.ytimg.com/vi/Byqqb35xODE/maxresdefault.jpg"><span style="text-transform: uppercase;">image/jpeg</span></a><span class="mwrapurl"><span>&nbsp;&#47;&nbsp;</span><a href="https://www.youtube.com/watch?v=Byqqb35xODE">URL</a></span></h1>
    <span class="msmall">3/2/25 8:00 AM</span>
</section>

But trying to edit the msg.contents or msg.url via javascript doesn't seem to work for this. Code used here:

function filterMessage() {
  // Check if msg.url exists and contains 'i.ytimg.com'
  if (msg.url && msg.url.includes('i.ytimg.com')) {
    // Replace 'i.ytimg.com' with 'inv.nadeko.net' in the image URL
    msg.img = msg.url.replace(/i\.ytimg\.com/g, 'inv.nadeko.net');
  }

  return MessageObject.Accept;
}