I have just updated my /etc/modprobe.d/nvidia-graphics-drivers.conf file to add the line below, hoping this will set the group permissions of the devices as I expect.
... options nvidia NVreg_DeviceFileGID=0
However, looking at /proc/driver/nvidia/params after a reboot, the group permissions are still set to a different user ID.
... DeviceFileGID: 1003 ...
What am I missing?