function mymodule_content_extra_fields($type_name)
This is EXACTLY what I was looking for. Thank you very much! Is there some API documentation on this? The only thing I've found is this article on Lullabot: http://www.lullabot.com/articles/great-pretender-making-your-data-act-field
You can use hook_field_extra_weights() to reorder fields via the cck manage fields screen like the flag module. You should be able to hook_form_alter a link to your own, custom settings page into that interface as a convenience.
I will definitely look into that. If hook_content_extra_fields() works, then that may not be necessary, but it doesn't hurt to give users more options.
In short, developpers list is for technical discussion, not "basic" questions.
How is that a basic question? -Karl.