3
As long as an upgrade consists only of new files (no database changes), I think it would be possible to go back to an old version.
You only have to keep track of which files have changed between the old version and the new version, and upload the original files (from the complete original distribution).
Never tried it, so it is on your own risk.
But the question is more, does it make sense to go back to an old version.
What kind of problems do you have? Are you sure that the problems come from version 2.0.6.
Maybe there has something other changed, but you didn't recognize.