[AT&T Samsung Galaxy S 4 Original Android Developme] ChaosMinionX:
Its quite an easy process, there isnt much that can go wrong. Just follow the instructions Ktoonsez posted, and make sure to use the "Wipe Data" button in the Wipe menu, and not the "Wipe/Advanced" menu to do it.

I did not restore data, I did a clean wipe of everything, I just TiBu from my External SD card.

EDIT: Here's the same instructions from KToonsez with a note at where I messed up so others dont, and also added instructions for making your ROM F2FS compatible.

First download latest Ktoonsez Kernel 4/28/2014, this provides the ability to convert your favorite ROM to F2FS compatibility, then follow these instructions.

Under "Tools" screen in KTweaker 7.0 go to the "F2FS: Convert ROM ZIP option". To use it, click that option, it opens a KT File Explorer, navigate to the folder where your zip files is, click the ROM zip file that needs converting and it will create a second file with the same exact name except adds a -F2FS to the end. A little hint, instead of using the back button once you are done converting, press the menu button and select close and KTweaker will remember that folder and take you right back the next time you go back in. It takes around 1:45 to do it my phone running ktoonsified v6, other profiles may take longer and if you are converting from external SD it may take longer depending on the quality of your SD.

Then get all the files from http://ktoonsez.jonathanjsimon.com/sgs4/F2FS/

(Should be 4 files, 2 files for EXT4 and 2 files for F2FS, this will just let you go back if you do not like, you can always ADB push the files you dont have if you just have recovery installed and no OS)

Once the above files have been downloaded proceed to the instructions below to get your phone formatted properly, make sure you have the F2FS converted ROM, and other KToonsez F2FS files/kernel/etc backed up to your External SD as you will be wiping Internal SD completely!

Original Instructions: http://ktoonsez.jonathanjsimon.com/sgs4/F2FS/Instructions.txt

********** Changing to F2FS w/ ROM**********

NOTE: Follow these steps EXACTLY, do NOT add or remove any steps, period!!!!

1. Backup everything from your internal SD to your PC or external SD, since the entire internal SD is going to get wiped out with format!!!!!!!!!!

2. Download the files from the folder that you got these instructions from and SAVE TO THE EXTERNAL SD!!!

3. Flash TWRP-KT-F2FS.zip (this is what gives us the ability to format using F2FS)

4. Reboot recovery

5. Go to "Wipe->Format Data" option, this option prompts you to enter "yes" into the box in order to proceed. Do not use Wipe>>Advanced Wipe option as this will not format /Data as F2FS and will cause a boot error stating "encryption unsuccessful" (THIS WIPES YOUR ENTIRE INTERNAL SD CARD, all files and folders, all gone so make a backup to your external SD or PC!!!!!!!!!!!!!)

6. Reboot recovery

7. Flash FormatCache-F2FS.zip

8. Reboot recovery

9. This step you have 2 choices:

A. Flash your ROM/gapps to start completely fresh

B. Go to restore option and ONLY restore your "Data"

10. Flash my newest kernel (needs to be a kernel dated 04.17.2014 or newer)

11. DONE!!!!!!!!!!!!!

12. A good way to make sure everything went good is boot back into recovery 1 last time and click the small "log" button in bottom center of the screen.

If there is no errors (like "unable to mount /cache" or "unable to mount /data").

If you have the /cache error, flash the Flash FormatCache-F2FS.zip, if you have the /data error, repeat steps 5, 6 and 7.