You will need to clone the MAC address of your old device to your new if you don’t want to loose your FlightAware stats. It is normally done by editing the /boot/cmdline.txt file and adding the following to the end of the line smsc95xx.macaddr=##:##:##:##:##:##
where ##:##:##:##:##:## is the MAC of your previous pi.
If you are using WiFi it is NOT the MAC of your WiFi but the MAC of the physical port on your Pi that is used for linking.