When I modify /etc/nsswitch.conf, is there an "nss" daemon I should restart? I am not referring to modules such as mdns & nis.
No you probably don't (other than what David said, and maybe ypbind, but you said not NIS). The nsswitch.conf file isn't for a daemon in particular, it is actually a file used by the C library for various system calls.
You may have nscd (Name Service Caching Daemon) running, which you may need to restart, otherwise it's unlikely. Certain daemons might cache get*() function call results and may need restarting.
Be aware that existing processes will not be aware of the changes to nsswitch.conf. The nsswitch.conf(5) page states, "Within each process that uses nsswitch.conf, the entire file is read only once; if the file is later changed, the process will continue using the old configuration."