I've run into a following roadblock removal of which should be intuitively
done combining two actions in one transactions:
- downgrading package A with brought package B on its preceding update
- removal of package B

This might have worked natively using "dnf history undo <transaction>"
where transaction refers to the one that previouslu updated A and brought
B as a new dependency, but unfortunately, the old packages are no longer
tracked in the (rawhide) repository.  This means I have to run:

dnf downgrade https://kojipkgs.fedoraproject.org//packages/A/...rpm

explicitly, but that will not remove package B along, not even after
I provide --allowerasing option to dnf.

What I would really need is to run a dnf transaction that is a composition
of two intertwined actions that will result in a dependencies-satisfying
state: downgrade + removal of particular package(s).

There does not seem to be any way to achieve this ATM.

In my particular case, packages are:
A:
mesa-{dri-drivers,filesystem,libEGL,libGL,libGLES,libgbm,libglapi,libwayland-egl,libEGL-devel,libGL-devel,libwayland-egl-devel
- new: 13.0.3-3.fc26, old: 13.0.3-2.fc26
B:
libglvnd-{glx,egl,devel}
and I am trying to check the circumstances of [bug 1413579 comment 14]

dnf version:
dnf-2.0.0-2.fc26.noarch