GPUOverVoltageOffset is read-only on GTX 660Ti?

Running 346.35 x86_64, Fedora 20, I’ve set CoolBits as explained in the readme so nvidia-settings now mentions GPUOverVoltageOffset:

nvidia-settings --query all | grep -i volt
Attribute ‘GPUCurrentCoreVoltage’ (buffy.sunnydale:0.0): 0.
‘GPUCurrentCoreVoltage’ is an integer attribute.
‘GPUCurrentCoreVoltage’ is a read-only attribute.
‘GPUCurrentCoreVoltage’ can use the following target types: X Screen, GPU.
Attribute ‘GPUOverVoltageOffset’ (buffy.sunnydale:0.0): 0.
The valid values for ‘GPUOverVoltageOffset’ are in the range 0 - 0 (inclusive).
‘GPUOverVoltageOffset’ is a read-only attribute.
‘GPUOverVoltageOffset’ can use the following target types: X Screen, GPU.

but it says it’s read-only and range 0-0. Should it be? I can change the voltage in MSI Afterburner in Windows but I don’t have Windows any more.
I need to do this because my factory-OCd XFX ‘Black Edition’ card crashes as soon as a game gets heavy, the internet suggested upping the voltage a tiny bit which seemed to fix it in Windows.

nvidia-bug-report.log.gz (227 KB)