Prior to raspbian stretch, the best way to configure an ethernet interface MAC address was within /etc/network/interfaces, adding the line
hwaddress ether 00:e0:4c:53:44:50.
At the moment I am having to set them via root crontab e.g.
@restart ifconfig eth1 down && ifconfig eth1 hw ether 00:e0:4c:53:44:50 && ifconfig eth1 up
Can I configure an interface within /etc/dhcpcd.conf to achieve the same result, as attempting the old way causes havoc.....