If you try to flash the stock MJ4 ROM after upgrading to KK, your phone will do nothing but reboot over and over, going no farther than the Galaxy note 3 splash screen. You CAN downgrade just the modem without bricking the phone, but I will tell you that when I did, I lost Wi-Fi. I have had horrible signal strength and signal since moving to KK 4.4.2. Even worse, something I didn't find out until after going to KK, SMS blockers won't work. Apparently there is something with the default messaging app where a notification will get sent no matter what to the default messaging app. So you'll get two notifications. You'll get get one in the blocker program and one in the default messaging app. Way to go Google on not preparing devs better, fail. Anyway, here is a link to a thread where you can get the MJ4 and NAB modems as well as the engineering bootloader. The stock bootloader is there too, but I think merely for entertainment purposes lol Anywho, here's the link http://forum.xda-developers.com/show...php?p=51165389
As I stated before, I lost Wi-Fi when I flashed MJ4. So just flash MJ4 first, then NAB, and you should see some........some improvement in signal strength.