on t400 running libreboot alter the ethernet mac address internally?

If a t400's flashchip got librebooted having the generic mac
address coming with the downloaded rom, can you then get
the computer's mac address on the flashchip by making
the rom cf
https://libreboot.org/docs/gnulinux/grub_cbfs.html#changeMAC
and flash it internally?

If yes, and the name of the new rom is
new.rom
what would the command look like?
Must you edit boot with iomem=relaxed? Thank you.