[libvirt-users] Accessing a MAC address from inside the VM?

Greetings, I have a very simple problem, but the resolution is proving rather complex. Bare with me, I will attempt to explain. I have a host machine with no GUI. I attach an existing .img file to the host machine and need to change the MAC address (since the image was created on another machine). Is there a way from with in the guest to do this or do I have muck with the XML? And if I muck with the XML and change it, how do I pass this information up to the guest, or will the guest see it automagically or do I have to write it down and then manually transfer it into the guest's ifcfg? Using the GUI, when you change the NIC, the guest generally does not see the new MAC and grouses until you change it. Thanks. DAVID