Flash unbranded/generic Stock ROM topic

Hello there,

I have bought Sony xperia z3 severals months ago. I'm happy with it.

I bought it from o2 Germany.
It's possible to flash/update the firmware to the unbranded/generic stock ROM? If yes, without losing DRM keys or other things and what can happen after flashing/updating to generic stock rom?

Some phone details as screenshots.

Attached Thumbnails