1. extract the 3 images, in one single directory,
  2. replace the updated packages (be careful to keep them in exactly the same RPM directories) (i have a script that does that, but can't access it now, sorry)
  3. regenerate the dependencies using misc/gendistrib script on CD1 (i'll get back later with the exact command)
  4. repack the CDs, keeping the original layout (use mkisofs) (i'll get the exact command later too :)
    (the CD name/labels need to be exactly the original ones, installer checks for them)
  5. (optional) add md5sums to ISOs, using misc/MakeCD script on CD1 Basically this will change only the Mandrake/RPMS and Mandrake/base (CD1), Mandrake/RPMS2 (CD2), Mandrake/RPMS3 (CD3)

IMPORTANT! This has (at least) one major weakness: the CDs will still boot the old original (buggy) kernel. To fix that, you have to repack the bootdisks, etc.