Updates all nodes of one type to be of another type.
$old_type: The current node type of the nodes.
$type: The new node type of the nodes.
The number of nodes whose node type field was modified.
function node_type_update_nodes($old_type, $type) {
return db_update('node')
->fields(array(
'type' => $type,
))
->condition('type', $old_type)
->execute();
}