This is very useful, and since the need to make ‘fake’ non-notifying @mentions is probably a power-user only feature, this might be all we need. Thanks @NateDhaliwal
Could probably make a custom markdown composer toolbar addon that wraps text in <a class="mention"> TEXT </a>. (I did see a TC or plugin that had that sort of custom functionality but I cannot remember which one it is!)
I have also been using an OS-wide tool called Espanso which auto-expands your custom abbreviations to whatever text you want, that could also be useful here for quickly inserting the HTML.