It's not the DRM keys that determine that - it's the state of the bootloader, whether it's locked or unlocked. You will have to block and avoid OTA (Over-The-Air) updates since those will soft-brick your phone with an unlocked bootloader. IIRC PCC and SUS will also refuse to recognize and communicate with your phone while the bootloader is unlocked, although Sony offers another tool to get you back on the stock firmware if you want it. Note that said tool does not relock the bootloader, nor does it restore your warranty.
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