need spec file example to replace files from various packages

[Paul Johnson]

After installing Fedora, I want to replace various configuration files
on lab computers. If I can learn how to do this in the post section of
an RPM spec file, I will be happy.  For example, I want/need to
replace things like

/etc/gdm/PreSession/Default
/etc/gdm/PostSession/Default
/etc/pam.d/system-auth
/etc/hosts.allow
/etc/hosts.deny

One brute force option is to install with rpm --replacefiles, but yum
does not like that.
So can  you point me at a spec file or two that will give example
syntax on how I can create a backup of those files and replace them
with the ones I want.

Please?

-- 
Paul E. Johnson
Professor, Political Science
1541 Lilac Lane, Room 504
University of Kansas