I figured out how to change my mac address of my network card:

sudo ip addr                                    # Show details

sudo ifconfig eth0 down                         # deactivate network card

sudo ifconfig eth0 hw ether DESIRED_MAC_ADDRESS # change mac address

sudo ifconfig eth0 up                           # activate network card

sudo ip addr                                    # show details again

What would be the best way to make this a script which I could start each time I need this modification? Also where do I have to put this generated script? What is the standard folder for this?

I don't want it to be started every time Ubuntu starts. (But it would be nice to know how this is done, though. Where would be the best place to store it in that case?)

Appreciate any suggestions!