How do I change / spoof my MAC address and easily switch between multiple ones?

First, go to the networking indicator and select "Edit connection" to configure a new connection:

Click 'add' and choose a name for the spoofed MAC network connection.

After selecting your interface "eth0" in the top dropdown, you can simply choose any MAC address you like:

And after connecting to it, you'll be using your new MAC address.

Running ip link ls will show you the new interface, including it's spoofed MAC:

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000
    link/ether 00:11:22:33:44:55 brd ff:ff:ff:ff:ff:ff

And now you can easily switch MAC-addresses by connecting to one of the new connections.

You can also change mac address on ubuntu or linux mint via the terminal

Go to your ubuntu or linux mint terminal, edit /etc/network/interfaces file

$ sudo nano /etc/network/interfaces

You should see something like this with dhcp enabled for your network interface. Usually its eth0 for ubuntu or linux mint wired network and wlan0 for ubuntu or linux mint wireless network.

auto eth0
iface eth0 inet dhcp

At the end of /etc/network/interfaces file, add this line to give your system’s network interface new MAC address.

hwaddress ether A4-19-E2-94-DD-BB

Save /etc/network/interfaces file with the new config, then restart your system network.

$ sudo /etc/init.d/networking restart

or

$ sudo service networking restart

You could try macchanger available in the repositories. Install with sudo apt-get install macchanger or through Ubuntu Software center.

$ macchanger
GNU MAC Changer
Usage: macchanger [options] device

Try `macchanger --help' for more options.
tvbox@tvbox-G31M-ES2L:~$ macchanger --help
GNU MAC Changer
Usage: macchanger [options] device

  -h,  --help                   Print this help
  -V,  --version                Print version and exit
  -s,  --show                   Print the MAC address and exit
  -e,  --ending                 Don't change the vendor bytes
  -a,  --another                Set random vendor MAC of the same kind
  -A                            Set random vendor MAC of any kind
  -p,  --permanent              Reset to original, permanent hardware MAC
  -r,  --random                 Set fully random MAC
  -l,  --list[=keyword]         Print known vendors
  -b,  --bia                    Pretend to be a burned-in-address
  -m,  --mac=XX:XX:XX:XX:XX:XX
       --mac XX:XX:XX:XX:XX:XX  Set the MAC XX:XX:XX:XX:XX:XX

Granted this a CLI utility.