Any configuration file that we need to change dynamically during installation (usually based on user input via debconf prompt - for example adding the user selected username or hostname to a configuration file) need to be handled via ucf. This will allow a user to be notified if there is any manual change in a configuration file during a package update. See manpages for ucf and ucfr for details.
Basically we keep our versions in /usr/lib and merge this with the actual version in /etc during postinst stage.