There's no good reason for the "unstable" version of spamassassin to
require unstable libraries, when the stable versions of those
libraries do just fine. I installed unstable's spamassassin with
--force-depends, but now the conflicts make apt-get unhappy.

Years ago I had a few lines of command from a friend that would let
one unpack a downloaded .deb file, modify the contents of the
directories that were created (to, f'rinstance, change a Requires
line) and repack the whole structure back into a new .deb with an
appropriate version number (in this case, a version that dpkg would
consider stable but later than the official "stable").

Can someone throw me a link?

Is this close to what you're looking for?

http://www.kitenet.net/programs/dpkg-repack/

I'm not sure this is exactly what you're after - the closest I've ever
been to Debian was through Knoppix. Hope it helps, though!

--seizer-ga

First get the build depences

apt-get build-dep foo

Then add unstable to your apt source list. Go to the directory where
you want to build all this... I use /usr/src

apt-get update
apt-get source foo

modify away

after your done modifing, go back to the /usr/src directory and

apt-get -b source foo

aptg-et will go check what the sources are and notice that they are
already in the doanloaded, then it will build the deb for you. (That's
what the -b does)  There is a dpkg option that will do it too, but I
cannot recall that right now.

Hope that helps,

-Jeff

PS - You should check the the Debian's irc channel #debian on
freenode.net  You might have to put up with rudeness, but there are
some real pros in there.