I was wondering if we could downgrade from Ubuntu 10.04 Lucid Lynx Alpha to Ubuntu 9.10 Karmic Koala. So I decided to put it upon test and I succeed. So, I am sharing this with those who wish to keep using stable Karmic Koala till the final version of Lucid is out.
Please note however, that all the installed applications will be lost, however the settings and files in your home directory will be preserved. So, for example if you have a huge list of saved sites on your Filezilla client, Filezilla will be gone, but when you install Filezilla on your Karmic, the settings should work. Also, your Firefox browsing history, preferences and other settings will also be preserved.