Extend CCK content type with a module - possible?

Hello!

Is it possible to extend CCK content types with custom modules that use the drupal hooks?
In my case I would like to add an item to the local tasks menu of my custom content type "persons".
I would like to write the module file content_persons.php containing the function content_persons_menu.
Is this possible? If not - how can I add a menu item to the local tasks of a custom content type?

Thanks,

Gabriel