[Q] Dirty flash 4.4.4 NJ5 to Lollipop?

My wife and I just purchased the AT&T US version Galaxy S4 I337 brand new in box with NJ5 4.4.4 firmware stock everything. No rooting nothing. Over the air updates brought in a 485 megabyte update three times. The first two failed, while the third attempt apparently succeeded.

I have checked updates twice since and it states "Current." In the "about phone" section it lists "Official" now.

I am EXTREMELY familiar with flashing custom and stock roms to my T-Mobile SGH-M919. I have downloaded the AT&T 5.0 Rom. Can I just dirty flash with Odin? Does the phone's locked bootloader prevent the Odin flash? Any tips or hints on this would be great.

I downgraded my T-mobile S4 to 4.4.2 from 4.4.4 with ease. With the AT&T be just as easy with the 4.4.4 to 5.0.1 with Lollipop?

cheers for any pointers or thoughts.

Problem with dirty flash older version of a custom rom

Hello, a friend of mine installed a custom rom at my lg g3 android phone. The rom is ressurrection remix. I accidently dirty flashed an older version of the same rom, I had 5.1.1 r6 and I flashed 5.0.3, and now neither adb works nor download mode due to killswitch. The only thing it does is show the old rr boot image. It's on a bootloop and since it doesn't open I don't know how to fix it. Can someone tell me what should I do? :)