This command in interface configuration mode will change the MAC address for a specific interface on the router.
And this is what I get when I use the show run command and view the properties of the interface.
interface FastEthernet0/0 mac-address 00de.00ad.00be ip address 192.168.0.1 255.255.255.0 ip nat inside ip nat enable ip virtual-reassembly duplex auto speed auto
The MAC address is shown this way. I am not sure why it is entered this way, but that is Cisco`s way of doing things.
And this is why you are more careful when assigning an IP address.
oberyn(config-if)#ip address 192.168.0.1 255.255.255.0 % 192.168.0.0 overlaps with FastEthernet0/0