Uninstalling a REPO?

I'd like to uninstall a repo -- not just the yum/apt/smart/etc. package
configuration for that repo -- but also all of the packages that came from that
repo.  But I'd also like to be left with a system that boots and runs as one
would expect.  And, finally, I'd like to avoid wiping my Fedora Core install and
reinstalling from scratch.

How easy is this to do?
Has anyone done this before?

I figure that if I remove the medley-package-config (which brought in a bunch of
repos, some of which are apparently incompatible with Fedora Core and Fedora
Extras) and then install the packages which are dependencies of
medley-package-config (like Firefox, X11, perl, etc.) that I need to have a
useful system, I should be okay.  But I'm guessing that this is not the case and
that I've overlooked something.  Any clues here?

Also, is any package manager good with doing this more easily?

  $ magic-package-manager --removerepo ATrpms
  $ magic-package-manage  --fix-my-broken-machine

It seems odd (and seriously bad) that it's so easy to add a new repo to one's
system, but so hard to remove the effects of that repo from one's system.

Thanks.