Comment # 46 on bug 1078466 from Aaron Puchert

Could we at least move /var/tmp to a separate file, so that admins can override
the cleanup interval without having to copy over the remaining entries?

According to the man page, "Files in /etc/tmpfiles.d override files with the
same name in /usr/lib/tmpfiles.d", so one can't just overwrite /var/tmp without
overwriting all the other subdirectories of /var.