;
Find the version of the package that you want to install. Often this will be in /var/cache/apt/archives if the new package was only recently installed. If not you can often get the old package from a mirror. Look under pool in the mirror eg [mirror]/pool/[packages].
Use dpkg -i package.deb for install the new lower version.
If there are dependencies on the newer version the package won't install. You have a choice of either forcing the install or downgrading the dependencies as well.