Respuestas:
Querrás usar taxonomy_save_term . La matriz que pasa a taxonomy_save_term debería tener este aspecto.
$term = array(
'name' => 'Taxonomy Term 1',
'vid' => 1, // The VID of the vocabulary this term should be saved under
'description' => 'A description of this term', // Not required
'weight' => 5, // Not required
);
taxonomy_save_term($term);