How to change ethernet card en0 MAC address ?
/how to do it from command line
and in c/c++ program ?
i doubt it can be changed in runtime, however it can be done on command line when starting/mounting the driver
Check with the EEPROM utility options.
I’ve written short script - chmac:
umount /dev/io-net/en$1
mount -v -Tio-net -v -o mac=$2,pci=$1 /lib/dll/devn-pcnet.so
use:
chmac 1 001122334455
it works, but it would be nice if I could change mac addr during en0 work 
Just a remark: I have observed that the umount command sometimes misbehaves in that it either stays blocked forever or it crashes io-net entirely. It happend with several drivers. Anybody seen this?
So I would not recommend to use this script in a production system unless thorough testing with known hardware has been done.
Regards,
Albrecht