Hi Pawel -
There are several methods of customizing the server interface, but the addition of out of context server administration tasks isn't one of them. If you're working within the framework of the server GUI, the menu options that are displayed on the tableau server interface are determined by the site role of the user signed in to the server. For example, if a server administrator or site administrator were to sign-in to the server, they would see options for USERS, GROUPS, SCHEDULES, TASKS, etc.; a site role other than those previously mentioned will not see these options.
Hi Pawel -
See here for the developer portal: Developer Portal
I wanted to confirm the change you've already made is not technically a change that is intended in Tableau Server - it won't be retained during an upgrade or a backup/restore of Tableau Server. Adding a url to the top bar is also not an available feature. If you'd like these added in the future, please add an Idea or vote on one that is already created on the Ideas forum: