Мак адрес

man ifconfig
hw class address
Set the hardware address of this interface, if the device driver supports this operation. The keyword must be followed by the name of the hardware class and the printable ASCII equivalent of the hardware address. Hardware classes currently supported include ether (Ethernet), ax25 (AMPR AX.25),ARCnet and netrom (AMPR NET/ROM).

пример
ifconfig eth0 down
ifconfig eth0 hw ether 00:08:54:12:C0:DA
ifconfig eth0 up
ну и поднять пропавшие маршруты если были