I want to remove this setting
Then do so - just use vi to edit it. But before editing, I do recommend you backup the current smb.conf file to a location where it won’t get wiped off after reboot - to say /usr/local/config/ and call it smb.conf.orig or something (although this file does get auto-generated at boot time so if you ever were to lose it, just rebooting will bring it back).
Keep in mind that your edited /etc/smb.conf will only last till your next reboot. If you either manually reboot or have firmware auto-update to ON a firmware update will automatically reboot the device (I believe) - and once rebooted your changes to smb.conf will be gone…so either you edit the file again to make your changes after a reboot or you also save a copy of your modified file to a reboot-persistent location (like /usr/local/config) and copy the file over quickly after a reboot for Samba to pick up the changes after a few seconds.
Samba process (smbd daemon) polls the smb.conf file so you won’t need to do anything beyond witng a few seconds after editing the file for your chages to take effect automatically. But if for some reason Samba doesn’t pick up the modified smb.conf file, see the last bullet point in this post -> http://community.wd.com/t5/WD-My-Cloud-EX2/Hacks-to-make-Public-share-and-USB-shares-private/m-p/728740#M408