Hello.
I have a Mesa Electronics 4i29 PC/104 ethernet card and I need to change the MAC address, because this network NEEDS that NIC have the same address (0080BFB0C453).
Recently I change this NIC and the actual had 00601B011260 address.
This is a driver option, for example with the ne2k driver:
io-net -d ne2000 mac=00ababcdcd01
for starting io-net and right away starting the driver for the NIC
or
mount -T io-net -o mac=12345678 devn-ne2000.so
for activating the driver while io-net is already running.
You need to unmount the NIC (assumed it is already in use) before manually overriding your mac (i think)
ifconfig en0 down
umount /dev/io-net/en0
mount -T io-net -o mac=15852539 devn-ne2000.so