Overrides can delete entries by not specifying a replacement field.

csv-generic/gen-generic.php

@@ -123,12 +123,16 @@ foreach ($lga_list as $lga) {
             $match_index = array_search($override['Match Field'], $header); 
             $replace_index = array_search($override['Replace Field'], $header); 
             if ($line[$match_index] === $override['Match Value']) {
+                if ($replace_index !== false)
                     $lines[$line_key][$replace_index] = $override['Replace Value'];
+                else /* If 'Replace Field' is not matched - delete this entry */
+                    $lines[$line_key]['Delete'] = 'y';
             }
         }
     }
 
     foreach ($lines as $line) {
+        if (isset($line['Delete'])) continue;
         if (fputcsv($handle, $line) === FALSE) {
             error_log('Error writing candidate to output file');
             exit(3);