I have a Cyclone V device already programmed with a non-volatile key. I now want to set the tamper protection bit. I have tried programming a .ekp that sets the relevant bit but the operation failed (because a non-volatile key was already present on the device). Is there another way?
Yes, non-volatile programming key is a one time programming only. I think there is no way to program the key already once non-volatile key is programmed.