Any way to dist-downgrade?

[Michael Yang <michael.yxf@gmail.com>]

Hi All:

Due to one hang issues of apitude, I upgraded my linux-images, but 
didn't resolve the issues.
Then I did "apt-get dist-upgrade", after which the aptitude issue is 
resolved, also after which more packages are upgraded that I didn't mean 
to. Now I want to keep only the kernel updated, but to downgrade the 
other packages to the previous one.

Now the source.list consists of the mirrors of "sid" dist, if I change 
it back to "testing", would there be any problems for the system?

Thanks a lot for your helps.
Michael.