I successfully upgrade to Singapore KitKat ROM (with root and knox 0x0) from SG JB (ML2, previously rooted and knox 0x0)
following method worked for me:
0. I was on Singapore firmware ML2
1. Download the SG ROM from sammobile.com
2. Copy the zip file to the root of your phone's internal SD
3. Disable reactivation lock under settings > security
4. Run Mobile Odin Pro. Allow SU access if prompted.
5. Load firmware in MOP
6. Enable EverRoot, Choose option "Download mode" in After flashing. Start flashing.
7. After booted into Download Mode, connect your phone to your computer and run Odin 3.09.
8. Load
N9005XXUENA6_BL-Only.tar.md5 in the BL section
9. Check
Phone Bootloader Update and
F.Reset.time, unchecked
Auto Reboot and Start Flashing.
10. When Odin says RESET!, switch off your phone and reboot normally.
11. boot into recovery mode and wipe the cache.
12. reflash the whole rom and choose automatic in "after flash".