Hi Nils,
good question! The default history setting for group-owned libraries is “keep full history”. So there is no need to enable it.
More generally speaking, only the department admin can manage the history settings of group-owned libraries. The department admin can change the history settings for group-owned libraries just like for any other library. Click on the advanced settings icon, choose “History Setting” and voilà (see below).
Last but not least, let me say this: I agree. System admins should also be able to change the history settings of department libraries.