…nt to base your configurable product. For example if you had a product that has size & colour as available configurable attributes and you just wanted to base your related simple products on the colour you would add one (or more) configurable attributes to the additional_attributes like this :

'additional_attributes' => array(
    array(
        'key' => 'config_attributes',
        'value' => 'some_attribute_code'
    )
),

…ready linked to the configurable product. (which throws a unique key error)

…on't go instead of removing those which are already there.

…t already exists with a different configurable attribute set, de product will be dropped and recreated. It works for me, use at your own risks!