Thanks guys for the solution.
$this->bbcode_second_pass_code('', 'fw_setenv ethaddr <mac>')
Where, <mac> is the mac address from the bottom sticker of your pogoplug device.
$this->bbcode_second_pass_code('', 'nano /etc/dhcpcd.conf')
Comment dduid
Uncomment clientid
It should look like:
$this->bbcode_second_pass_code('', '
# Use the hardware address of the interface for the Client ID.
clientid
# or
# Use the same DUID + IAID as set in DHCPv6 for DHCPv4 ClientID as per RFC4361.
# duid
')
then,
$this->bbcode_second_pass_code('', 'reboot')
Your original mac address should be back