I tried to add a parameter to the following code and it does not work.

Thats because that code is unorganized and full of "Red flags".

Organize your code, box up everything into subroutines (Every loop, every heredoc template, every giant if/else block).

This is a "Red flag" localtime ... $year + 1900, . Time::Piece and DateTime is what you want to use for date stamps/math, none of this +1900 stuff.

You would benefit heavily from reading "Red flag" as it was written exactly for you. Almost every example is one you have posted here.

Subroutines should take arguments not work on globals. You shouldn't mix who prints from where....

This is something like what your program should end up looking like

Main( @ARGV );
exit( 0 );
sub Main {
    my $pms = empire->new;
    my $query = CGI->new;
    my( $header, $body ) = Dispatch( $pms, $query );
    print $header, $body;
}
sub Dispatch {
    my( $pms, $q ) = @_;
    if( $pms->authenticate( $q ) ){
        my $page = $q->page || 'default';
        return ThisPage( $pms, $q  ) if $page eq 'thisone';
        return ThatPage( $pms, $q  ) if $page eq 'thatone';
        return DefaultPage( $pms, $q );
    } else {
        return UnauthorizedPage( $pqms, $q );
    }
}
sub UnauthorizedPage {
    my( $pms, $q ) = @_;
    return RedirectTo($q, 'notloggedin.cgi');
}
sub RedirectTo {
    my( $q , $page ) = @_;
    my $header = $q->redirect( UrlFor( $page ) );
    my $body = '';
    return $header, $body;
}
sub UrlFor {
    my( $name ) = @_;
    return $name; 
}
sub DefaultPage {
    my( $pms, $q ) = @_;
    my $members  = $pms->list_members;
    my $schedule = $pms->campaign_schedule;
    return $q->header, CampaignMembersHtml( $pms, $q, $members, $sched
+ule );
}
sub CampaignMembersHtml {
    my( $pms, $q, $members, $schedule ) = @_;
    my $html = MembersHtml( $q, $members );
    $html   .= ScheduleHtml( $q, $schedule );
    return $html;
}
sub MembersHtml {
    ...;
}
sub ScheduleHtml {
    my( $q, $schedule ) =@_;
    my (
        $status,
        $schedule_date,
        $max_emails,
        $clast60,
        $aolflag,
        $openflag,
        $yaho­o_flag,
        $shour,
        $smin,
        $old_mid,
        $old_dname,
        $cname,
    ) = @$schedule;
    ...;
    return $html;
}
sub Empire::authenticate {
    my( $pms, $query ) = @_;
    my $user = $query->param('user');
    my $pass = $query->param('pass');
    return !! $pms->check_security( $user, $pass )
}
sub Empire::list_members {
    my( $pms, $q ) = @_;
    ...
    my $members = $dbh->selectall_arrayref($sql);
    ...
    return $members;
}
sub Empire::campaign_schedule {
    my( $pms, $q ) = @_;
    ...
    my $schedule = $dbh->selectall_arrayref($sql);
    ...
    return $schedule;
}
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