Ok. Answering my own question as I figured it out and someone else may benefit.
Edit files:
/etc/init/smbd.conf
/etc/init/nmbd.conf
and insert -s /usr/syno/etc/smb.conf.NEW, for both smbd and nmbd exec strings, whereas *.NEW contains customized smb conf, save & reboot.. All is well with my samba tweaks.