After several hours of trial and error, I found a way that worked for me. It will trip the Knox counter though. Also, what worked for me may not work for everyone else. If you brick your device that's not my fault in any way, so good luck :D
Using this guide, flash back to the stock TAR (not the UVUAMDL TAR). This restores 4.2.2, which allows access to the menu. However, this alone is not enough, as it won't give you access to the perso functions. Attempting to flash the UVUAMDL TAR will result in an error (at least, it did for me).
Second, extract the modem.bin from the UVUAMDL file, and flashed it to the phone using Odin. It's similar to the guide above, but instead of using PDA, you use phone. This gives you access to the perso functions, as it forces the baseband back to UVUAMDL from UVUEMK2. It may be possible to flash the UVUAMDL.tar modem files found in other threads, I haven't tried this out myself though.
Now, at this point you can follow the
instructions in this thread, as every option should now be available. If they're not, make sure your Android version is 4.2.2 and that the baseband is UVUAMDL.
If it works at this point, great, go on to the next step (you may have noticed by now that your sound is not working). If not, use
RegionLock Away to fully unlock the phone. At this point, your phone should be fully unlocked and you can see it connected to the network. However, dialing/calling lags significantly, and there is no sound.
The next step is to use Odin to fully restore UVUEMK2, which would restore full functionality. You can download the file from
here, and flash using the same steps above. This will restore full sound and phone functionality, while your device remains unlocked. If it gets stuck during the boot animation, you simply need to do a factory wipe from recovery (not sure if this works, haven't tested it myself), or just install your recovery of choice from Odin and install whatever ROM you want to use (what I did, which still required a full factory reset from recovery). Skipping restoring UVUEMK2 and installing your ROM of choice does not work, however. You will still have no sound and the phone function will lag considerably.
If everything goes well, you should have a fully unlocked T-mobile Galaxy S4.
