[NTLUG:Discuss] Creating distro install disks with updates

[Leroy Tennison]

I'm wanting to create a CentOS 5 DVD containing the current updates to 
the RPMS.  I already have the original DVD.  I'm hoping all I need to do is:

mount the original dvd image using -o loop
download the updated rpms from an update mirror
copy the updated rpms over the mounted image rpms, overwriting as needed
umount the image
burn the result

Is there anything I'm missing?  MD5 or SHA1 sums somewhere that the 
installation checks?  Do I need to update the repodata files?

Any insight would be most appreciated.