In response to how to set a NIC's MAC address asked on another forum [Astaro wants gear-head answers confined to this forum]:
ifconfig ethwhatever hw ether mac address
This is really a basic Linux question; a search returned the answer right away for me. I didn't mind at all answering it, but maybe you will find it quicker if you just try that first next time.
To know to do the search, you did have to know that the ifconfig command governs network interfaces. If you didn't know that, I would like to recommend "Advanced Linux Networking" [publisher Addison-Wesley] to come up to speed. In spite of its name, it is actually easy to follow, and has much useful information on the proxies that Astaro runs.
You will have to put that in one of the boot startup scripts in /sbin/init.d; check with more searches, or look at what's in that directory to start coming to an understanding of this distro's boot process.
Or if you're still hitting your head against the wall, ask another question of one of us on this forum...