apt - How can I downgrade packages without removing their dependants?

I have a number of mesa packages that I had upgraded to a PPA version, before purging the PPA so I could upgrade my system. The differences in the versions are minor (they are technically the same, just one set of libraries were from git and the others are the final versions).

If I try to downgrade via Synaptic, apt-get, or aptitude, I get thrown into dependency hell.

Is there a way to downgrade the packages manually (perhaps one by one) and mark their dependant packages as immovable (if that makes sense) until I am done?

P.S. this question: How to Downgrade a Package via apt-get? is a bit different and doesn't help this situation.

I never played with this before, but I would suggest that you hold (or lock) the version of the dependencies that cause you trouble. This way apt has a more limited number of possible solutions, and perhaps doesn't get confused when you attempt to downgrade the other packages.

---

If nothing else works, you could take the manual approach suggested in this answer: How to Downgrade a Package via apt-get?. Basically, download the necessary .deb packages manually, then install them one by one using the lower-level dpkg and one of its forceful arguments: --ignore-depends, --force-depends, --force-depends-version, or even --force-all.

In the same spirit as the above, you have the --force-downgrade argument:

          downgrade(*): Install a package, even if newer version of
          it is already installed.

          Warning:  At  present  dpkg  does  not  do any dependency
          checking on downgrades and therefore will not warn you if
          the  downgrade  breaks the dependency of some other pack‐
          age. This can  have  serious  side  effects,  downgrading
          essential system components can even make your whole sys‐
          tem unusable. Use with care.

But this assumes that you've read man dpkg, and that you understand what you do:

          Warning: These options are mostly intended to be used  by
          experts  only.  Using  them  without  fully understanding
          their effects may break your whole system.

See Error: version number does not start with digit and How to install an older version of Java and How to install a older version of package like liquid 2.2.2? for examples of:

sudo dpkg --force-downgrade -i your_mesa_package.deb

And see How can I install a package without installing some dependencies? for an example (along with the appropriate warning) of:

sudo dpkg --force-all -i your_mesa_package.deb

---

Yet another approach would be to create a dummy .deb package using the equivs package (and perhaps a slightly different name). Then installing the dummy package should allow you to remove the "true" package while keeping the relevant deps, and then install the older version. I'm not sure how exactly this would work, but check this relevant thread for details: How to remove a deb without removing its dependencies.