In AIX land, the authentication order is dictated by the file /etc/netsvc.conf. Most other flavors use /etc/nsswitch.conf. Any changes you make in there, once you save, become effective immediately.
All that said, the best thing is to not have two same account names even if one is local and one is NIS. If you look at /etc/passwd, and your setup as an NIS client, the +::0:0::: tells ypbind to auth against your NIS domain master. If you netsvc.conf is default, any account above +::0:0::: will authenticate locally first, naturally, if the local account doesn't exit, system will then auth against your NIS domain.
I would rename batman to batman_local or batlocal. This way you have your local account (above +::0:0::
and also helps administration wise knowing that batlocal is local and not NIS.
Good luck!