How do you properly fork a Linux distro?
I was wondering, how one would go about creating a Linux distro. LFS seems like overkill, I would rather fork an existing distro. I know there are several "respin" applications, but these only seem to allow you to add extra applications to be installed, they don't seem to allow you to modify repositories, configs, and etc etc.
What I'm looking for is knowledge on how to take an existing distro, and modify it significantly, ideally by modifying Fedora or Mint, although I might need to use an older kernel.
General advice is appreciated, how would you modify the files it ships with? What tools do you use? How would you wrap it into a liveCD? How do you host a repository?