Since the Knox warranty bit is now 1, that means the warranty has been manufacturer's has been voided. Not a big deal if the warranty on your phone is over.
Now that your phone has the 4.3 bootloader, you cannot flash any ROM via Odin, TWRP, or CWM that attempts to downgrade the bootloader. Attempts to downgrade could brick your phone.
You may be able to flash back to mk5 using Mobile Odin.