Question

Is it possible in code (or manually) to create a Product Attribute that is not visible (and thus not editable) through the administration edit product page? And how?

(The attribute only needs to used (save / load) in php modules)

Answer 1

Yes, it is possible. If you doing it in install script – you should set 'visible' to false:

$installer->addAttribute(Mage_Catalog_Model_Product::ENTITY, '<attribute_code>', array(
    ...
    'visible'       => false,
    ...
));

If you need change it for existent attribute directly in db – go to catalog_eav_attribute table, find your attribute (look for attribute id by attribute code in eav_attribute table) and set it’s is_visible field to 0.