For now this has to be done after flashing your preferred firmware (ROM). I recommend you make all your desired changes especially changing kernels.
Copy the files to your sdcard where you typically put flash files. I recommend an external card, because this is the only way I do it and I have not tested the other way. If you put it on your internal card it needs to be outside the /system and /data partitions because you'll lose them during formatting.
Also, I have only tested this on PhilZ Touch 6.58.9 recovery. I would appreciate anyone testing on other recoveries if you find one that supports f2fs.
If you are not on PhilZ 6.58.9, flash the zip and reboot to recovery.
Make a full back up of your ROM.
I also recommend you have an Odin based recovery plan. During my trials I ended up with a blank screen and used Odin to get back. This may not be the case with this latest PhilZ.
Format the partitions to f2fs.
It is in "Wipe and Format Options", then "Custom Format Options" then "Toggle f2fs <-> ext4 migration"
Remember, to format data you pick /sdcard. Also, this will remove everything on your internal card.
See warnings in post #2
I include a testF2FS zip to confirm the formatting.
Then use custom restore to get the data and/or the system from the backup. You can skip cache since it gets rebuilt.
Then flash GS3-F2FS-kernel-fstab-Fixer to adjust the kernel boot image to support the new formats.
This only fixes the fstab and if the kernel does not have f2fs support it will not work.
As always, no one is responsible for what happens to your phone. Everyone does this on their own and at their own risk.
Please do NOT mirror these files.
It appears to only work with the PhilZ recovery I built. If someone finds another please let us know.
Also, it does not work on TouchWiz ROMs. If someone finds one that it does work on please let us know.
Do not use the phone setting Factory Data Reset
F2FS, Tool/Utility for the AT&T Samsung Galaxy S III
Beta Release Date: 2014-11-13
Last Updated 2014-12-06