Hi i changed the mac and Serial by editing the file that resides on the USB...
File is located under boot\grub\grub.conf
this is what mine looks like
#serial --unit=0 --speed=115200
#terminal serial
default 1
timeout 4
hiddenmenu
fallback 0
title SYNOLOGY_1
root (hd0,0)
hw_model
kernel /zImage root=/dev/md0 ihd_num=5 netif_num=1 syno_hw_version=RS3612xs
initrd /rd.gz
title SYNOLOGY_2
root (hd0,1)
# cksum /grub_cksum.syno
# vender /vender
# hw_model
kernel /zImage root=/dev/md0 ihd_num=5 netif_num=1 syno_hw_version=RS3612xs mac1=00113205V7U8 sn=B7J4N00000
initrd /rd.gz
All you need to do is add the MAC and Serial number.. please note the mac address format.. 00-11-32-05-C8-7B will not work.
to edit the file on windows i used notepad++ which is free to download.