I have an iMac mid 2011 with Maverick which i have replaced with a iMac retina 27" with Yosemite Preinstalled. I did a Migration Assistant to transfer files from old to new mac. Now i want to downgrade the new machine from Yosemite to Mavericks. Can i use a TM backup from the old machine made AFTER the migration, to do this? (Using the OS X Utilities restoring from TM Backup).
Doubtful, the minimum OS for the 27" iMac is 10.10. You can lay the TM backup down on the iMac, but it will most likely panic on the subsequent reboot.