By default date and time is displayed by the clock applet on the top right of the gnome desktop in Ubuntu. For me this displays something like "Tue Aug 3, 19:45". I would like to change it to make the date terser and to include e.g., ISO week number - to something like 03/08-19:45-W31.2

Is there anyway I can specify a "format string" for how the date-time is displayed ?