Downgrading a package
From MEPIS Documentation Wiki
Use of Synaptic to downgrade a package may be easier for some users, see the User's Manual.
A specific version of a package can be selected for installation by following the package name with an equals and the version of the package to select. This will cause that version to be located and selected for install. Alternatively a specific distribution can be selected by following the package name with a slash and the version of the distribution or the Archive name (stable, testing, unstable).
apt-get install packagename=2.11 apt-get install packagename/testing