I've been tinkering with it a bit more. Found out NVRAM settings can be modified in OS X Terminal app (nvram command).
That is the normal way to control Open Firmware when X is installed. It is still used on Intel and ARM macs to control boot variables, where there is no OF.
Note that it only works when you sudo to the root user.
Of course holding down OPT+CMD+P+R at boot still resets it,
So what did you expect? You asked it to clear nvram. That is what command-option-P-R does.
1: "Doctor, it hurts when I do this!"
2: "So stop doing it."
but I wonder if I write-protect usr/sbin/nvram after modifying it -- and obviously testing it a billion times before doing so -- what would happen? Do you think it would brick?
This modification is not a must, but just something I'm curious about.
Makes no sense. The /usr/sbin/nvram is just the command line program. Boot variables are not stored
inside it. They are stored in (drum roll) non-volatile memory. And that cannot be write protected, at all.
You can't "brick" a computer by changing its boot variables because there are ways to interrupt the boot process to regain control. The chief one being command-option-O-F on PowerPC.