would adding the kernel parameter elevator=noop
do the same thing without having to go about all of the script stuff?
Forget that. You can't set it for just one drive using the kernel parameter. It would set it for all drives.
and you are correct..
Just create the create the /etc/rc.d/rc.local file and make it executable via chmod.
If systemd doesn't automatically pick it up once it is created and set executable, the try enabling the rc-local.service.
systemctl enable rc-local.service