Quicksilver 2002: OpenFirmware and default graphics card

[Super Bisquit <superbisquit%gmail.com@localhost>]

I see that there is a forth command of probing the scsi with a value of -1.
The agp slot resides at pci@f000000- I may be missing a number, please forgive- along with pci0.
On this machine, I am running Debian, FreeBSD, and attempting to add NetBSD to the mix.

I'd like to switch the default card from the agp slot of a Radeon 7500 to  a Matrox PCI- 64bit, 33MHz isa-pci?- 
without having to physically remove the cards.

Open Firmware command pages do not cover the process in detail, at least not what I have seen in my searches.

What is the forth command to enable such?