Change the login button link/pop up

I’ve tried to do this too but I think I’ve missed something as nothing happens upon clicking with this script:

<script> 
  var loginButton = document.getElementsByClassName("header-login-button");
  loginButton[0].setAttribute('href', '/topic/new');
  loginButton[0].removeAttribute('data-modal');
  loginButton[0].setAttribute('class', 'header-login-button qa-header-login-button btn btn--secondary');
</script> 

(Using topic/new to test...)

And yet the resulting code looks exactly the same as what is on the Zapier community login button!?!?! I’d love some input!

@SmartlyGreg 

This is what I have currently under ‘Third Party Scripts’ → ‘Before </Body>’

<script>
// Mutator observer to check for changes in the login modal and kick of SSO flow
function callback(mutationList, observer) {
  if (inSidedData.user.role === 'roles.guest') {
      window.location = '/ssoproxy/login?ssoType=openidconnect&returnUrl=' + encodeURIComponent(window.location.href);
  }
}

const targetNode = document.querySelector(".qa-login-modal");
const observerOptions = {
  childList: true,
  attributes: true,

  // Omit (or set to false) to observe only changes to the parent node
  //subtree: true
}

const observer = new MutationObserver(callback);
observer.observe(targetNode, observerOptions);
</script>

Actually this script was added by the insided support team. Based on which login type you are planning for SSO you can change the ssoType parameter.