That would be news if it was true, but it isn't. You cannot revert from one
version to a lower one. Once 10.10 is installed it will replace all of the
root file structure nad it changes the sources list to the new version. If
you have a separate home partition or do an upgrade as opposed to a fresh
installation then it will keep your data and settings. The only way to get
it back to 10.04 (there is no 10.4 BTW) is to do a fresh installation. Many
distributions have been working on a roll back feature, but it is just a
pipe dream thus far. You can roll back parts by apt pinning, but not the
full distribution (at least there is no recommended way).

http://brainstorm.ubuntu.com/item/9625/
https://answers.launchpad.net/ubuntu/+question/18176

You are free to try, but it isn't for the feint of heart and the risk is all
yours. Considering that it takes only 20 minutes to re-install and the
outcome of doing the rollback as shown below could be messy and the results
are iffy at best, it seems to be a major time waster.

https://help.ubuntu.com/community/DowngradeHowto