I've tried via EPST (using both ##MSL# and ##3282#) and whenever I change either of those two options and Commit changes, it says "Commit Failed".
I've tried through PC with DIAG mode, but diag mode seems to be absent in 5.0 and after I downgraded to 4.3 and "activated" diag mode, it never showed up on my PC or in device manager. Plus in QPST, i can't activate any COM ports because of the "The port may not be working or may be busy. (-2147467256)" error.
I'm using a Windows 8.1 PC and my phone is currently on the 3.05.651.6 OTA.