Note: After saving, you have to bypass your browser's cache to see the changes. Google Chrome, Firefox, Microsoft Edge and Safari: Hold down the ⇧ Shift key and click the Reload toolbar button. For details and instructions about other browsers, see Wikipedia:Bypass your cache.
addPortletLink(
  "p-personal", //Indicates where the link goes- the top bar, in this case
  "https://meta.wikimedia.org/wiki/Steward_requests/Username_changes#Dakarias.40global",
  "Username change status",
  "Custom link ID- you can leave this the way it is",
  "HRNG",
  "", //I'm still not sure what this does, to be honest- feel free to experiment using a copy of this script.
  document.getElementById("pt-logout")); //Adds the link before the Log out button.