No idea how to make it permanent.Ah. I could give that a try. The better question then, is there a way with root to make this change permanent? I recall that removing the SIM card or applying a system update undoes the changes to that XML file.
Additionally, can you elaborate on the "setprob sys.usb" part? I'm not sure what you'd mean by that since yeah we do now lack EngineerMode.
adb shell -> su -> setprob command
I don't recall what the command is exactly but try this: https://forum.xda-developers.com/t/diag-mode-qpst-functionality.4247843/post-85536271