Changing MAC Address and undoing changes
To your first question "is it permanent"-- 

No it is not, it will revert to the original when you restart. 

The reason is a MAC address is given to a network adapter (card) when it is manufactured. It is hardwired or hard-coded onto your computer's network interface card (NIC) and is unique to it, so when you restart system will get the hardwired MAC address from the network card. 

However there are ways to keep it permanent, but that is another question and method.

To your second question:

OS X uses en0 and en1 to identify the network type.

Depending on the configuration those could be:

en0 for the Ethernet (cable) interface

en1 for the WiFi interface

But it is better to look up your specific configuration. 

To find out the currently used MAC address run ifconfig en1 | grep ether or ifconfig en0 | grep ether in your Terminal app.