vsi: just learn to make the cloning, therefor, you can always test things b4 bricking anything... cloning takes about ~10 mins roughly, and copies entire system (exlcuding bootloaders)
if you intend to run osx on a seperate hdd (i higly suggest that!!!), just prepare your hdd with 3 partitions minimum!!!
1- for main partition system (once you made everything working)
2- test partition system
3- backup/downloads etc... partition system
and use mbr partition scheme... dealing with guid is more of a pain than a real gain... guid is intended for server systems... and there are many things to worry about all the time if u use guid...
cloning is easy... open disk utility, choose restore, use main partition as source, and test partition as target/destination, and (dont choose erase during cloning, always erase the test partition before you start cloning, bcoz it will clone the name if you choose the erase in restore function, which may confuse you later!)
in about 10 mins it will finish... like i said, it copies entire system, except bootloader... any you dont need a bootloader on the same hdd twice
bcoz original bootloader (if you dont delete the partition by accident) will let you boot the test partition as well!!!
all you do is press f8 at countdown screen, and choose test partition, it will boot... do all your testing there, w/o worrying about bricking it... once you learn how to do whatever you wanted to do, then apply it on the original one...
understand that once you have a workinng test partition, dont clone the test partition back to main system... you will erase the bootloader and it can be a pain to bring it back if you dont know what to do... (if you have iatkos r3 dvd, it is easy to restore bootloader
just boot of the r3, and choose only efi bootloader in the customize window, and deselect everything else... and install, tata bootloader working again
make sure you dont select anything else!)
everytime you learned how to update your system without bricking it, make sure you do a back up of the entire system... i m not sure timemachine backs up entire system with the bootloaders... but make sure you back up importtant stuffs...