No you cannot generally migrate everything back to a lower OS and if you attempt to run any installer that is older than the installed OS, it will error and tell you it won't even start the install.
But if you don't mind hand migrating documents or making a new backup (as opposed to settings and internal database files), the answer shifts to yes by erasing the new OS and starting new on the older installer.
Apple publicly explains how to erase your Mac and reinstall a lower version of OS X on the Public Yosemite Seed FAQ page:
Specifically the part where it states:
What if I have problems running the pre-release software? :
If you must remove the beta software from your computer, you will need to erase, install, and restore the Time Machine backup of Mavericks that you created before you installed the OS X Yosemite Beta. Any changes to your files and documents since you installed the OS X Yosemite Beta will not be preserved when restoring your Mavericks backup, so be sure to copy any new or changed files before you begin restoring from your Mavericks backup.
It then links to the Apple support articles below: