Concerning adding a f12 system beside your current setup. If you have enough space on the HDD, I'd backup your f11 system to a tar, resize your f11 partition, and create one for your f12 system. Once your satisfied with f12 you can "rm" the f11 system and copy the f12 system onto its partition and then reclaim the space used for the initial f12 install or leave it there for future situations like this one.
Taring your f11 system is really easy if it isn't spread across multiple partitions. Some documentation to get you started on the tar'ing process. https://help.ubuntu.com/community/BackupYourSystem/TAR
the backup tar is quite easy to make. Restoring can involve updating your /etc/fstab for the new disk location and possibly reinstalling/fixing your grub/grub configuration or what ever bootloader is used for the Mac version.
Concerning apple hardware, I touch it as little as possible.
-Will