dsl - n55u smb.conf howto make persistent?

i need to add this line into /etc/smb.conf to make directory writeable otherwise a camera cannot write..
at every reboot the file was overwritten.. anyone could help me?
force create mask = 0777
force directory mask = 0777
create mask = 0777
security mask = 0777
force security mode = 0777
directory mask = 0777
directory security mask = 0777
force directory security mode = 0777