In modern Linux distributions, there is a special directory named /etc/default which holds the default configuration informations on some services, programs etc.
For example on a Debian based system, you can set
TMPTIME=7
FSCKFIX=yes
in /etc/default/rcS so that your system holds files in /tmp directory not older than 7 days and makes automatic fsck fix when a problem exists on disk.
Or you can set
GROUP=500
in /etc/default/useradd so that your newly created users have 500 group id in default.
There are more, just look at contents of /etc/default