What is "downgrading a system"?

In Debian world, it means to move to an older distribution (typically, to move from unstable to testing). Do not expect to get anything stable by downgrading!

Is it supported?

So, what's the supported way?

  1. Make a backup of your system before you upgrade, so you can restore your backup to "downgrade" it !
  2. or Re-install.

How to downgrade a system?

Be warned: you will be alone! However, Auke Jilderda wrote about the experience back in 2002: http://people.debian.org/~osamu/pub/downgrade.html (plus some comments from Osamu Aoki)