I would really like to be able to "pin" ebuilds to a certain version so that
they are never upgraded or downgraded. This could either be done via a
/var/cache/edb/pin file or by allowing >=/=/etc support in world. I'd be
willing to add this functionality myself if there is any interest in it, though
I don't know the portage code well.
you can already pin apps in the world file.
quoting from: http://www.gentoo.org/doc/en/portage-manual.xml
An interesting entry to note is the entry for the mozilla package
(=net-www/mozilla-0.9.8-r3). This entry was added manually by a user to "pin" a
specific version. Package ranges (as discussed in the Unmerge Packages section
of this manual) can be used to force Portage to only consider certain version
ranges when updating packages. This entry in effect "pins" Portage into
considering mozilla-0.9.8-r3 to be the only available version and thus it will
never attempt to update the package during a world update for any reason.
Well, color me embarassed.