Add data to OAI-PMH export

LocalDC.pm

# THIS IS UNTESTED
# try it on a test server first!
#
# Save file to: ~/archives/ARCHIVEID/cfg/plugins/EPrints/Plugin/Export/LocalDC.pm
# then run:
# > bin/epadmin test ARCHIVEID
# if there are no errors, add the file below and run it again.
# if there are still no errors, restart apache and test the OAI-PMH interface.

package EPrints::Plugin::Export::LocalDC;
@ISA = ( 'EPrints::Plugin::Export::DC' );

use strict;

sub convert_dataobj
{
        my( $plugin, $eprint ) = @_;

        my @dcdata = $plugin->SUPER::convert_dataobj( $eprint );

        # add isbn
        push @dcdata, $plugin->simple_value( $eprint, isbn => "identifier" );
        
        # add doi/id_number (field usage may vary!)
        push @dcdata, $plugin->simple_value( $eprint, id_number => "identifier" );
        push @dcdata, $plugin->simple_value( $eprint, doi => "identifier" );

        return \@dcdata
}

1;

z_plugins_oai.pl

# THIS IS UNTESTED
# try it on a test server first!
#
# Save file to: ~/archives/ARCHIVEID/cfg/cfg.d/z_plugins_oai.pl
#
# Alias the new plugin to the old one:
$c->{plugin_alias_map}->{"Export::DC"} = "Export::LocalDC";
$c->{plugin_alias_map}->{"Export::LocalDC"} = undef;

Hello, finally I tried but it doesn't work.
I had to change the main DC.pm file.