Hi Christoph,
For most objects any change to the HTML5 UI will be directly reflected to the Responsive UI. The Ticket object is an exception, as the mobile floorplan used in the Responsive UI is different from the desktop floorplan (aka Agent Workspace) used in HTML5.
Till release 1602, in oder to reach the mobile floorplan from HTML5 (and personalize/adapt it) the admin had to tweak the URL by adding "&sapbyd-agent=TAB", as recommended by Sanath above.
Starting with release 1605, when you adapt the Ticket (desktop) UI in HTML5, you will see a link at the top of the page to open the mobile floorplan. If you have access to a Test tenant, you can probably already test it as the tenant should have been upgraded by now.
Kind regards,
Gab