add_action( 'init', 'wpa4182_init');
function wpa4182_init()
{
global $wp_taxonomies;
$wp_taxonomies['category']->labels = (object)array(
'name' => 'Simple post taxonomy',
'menu_name' => 'Simple post taxonomy',
'singular_name' => 'Simple post taxonomy',
'search_items' => 'Search Simple post taxonomy',
'popular_items' => 'Popular Simple post taxonomy',
'all_items' => 'All Simple post taxonomy',
'parent_item' => null, // Tags aren't hierarchical
'parent_item_colon' => null,
'edit_item' => 'Edit Simple post taxonomy',
'update_item' => 'Update Simple post taxonomy',
'add_new_item' => 'Add new Simple post taxonomy',
'new_item_name' => 'New Simple post taxonomy',
'separate_items_with_commas' => 'Separata Simple post taxonomy with commas',
'add_or_remove_items' => 'Add or remove Simple post taxonomy',
'choose_from_most_used' => 'Choose from the most used Simple post taxonomy',
);
$wp_taxonomies['post_tag']->label = 'Simple post taxonomy';
}