Change Post Name Labels

I am looking to rename the post type labels set when using register_post_type to a different name – from Whistle(s) to Snippet(s). This can be done it seems with the following filter:

post_type_labels_whistle

I gave this a go with the following code in my theme functions.php file:

function pxlcore_whistles_post_labels( $labels ) {

	$labels = array(
		'name'               => __( 'Snippets',                   'whistles' ),
		'singular_name'      => __( 'Snippet',                    'whistles' ),
		'menu_name'          => __( 'Snippets',                   'whistles' ),
		'name_admin_bar'     => __( 'Snippet',                    'whistles' ),
		'add_new'            => __( 'Add New',                    'whistles' ),
		'add_new_item'       => __( 'Add New Snippet',            'whistles' ),
		'edit_item'          => __( 'Edit Snippet',               'whistles' ),
		'new_item'           => __( 'New Snippet',                'whistles' ),
		'view_item'          => __( 'View Snippet',               'whistles' ),
		'search_items'       => __( 'Search Snippets',            'whistles' ),
		'not_found'          => __( 'No snippets found',          'whistles' ),
		'not_found_in_trash' => __( 'No snippets found in trash', 'whistles' ),
		'all_items'          => __( 'Snippets',                   'whistles' ),
	);

	return $labels;
}

add_filter( 'post_type_labels_whistle', 'pxlcore_whistles_post_labels' );

All that happened was all the labels disappeared. On further investigation is seems that the $labels passed to the filter are an object class not an array which is what I was pushing back to the filter. I suspect this is why it fails. The object class passed is:

object(stdClass)#107 (14) {
  ["name"]=>"Whistles"
  ["singular_name"]=>"Whistle"
  ["add_new"]=>"Add New"
  ["add_new_item"]=>"Add New Whistle"
  ["edit_item"]=>"Edit Whistle"
  ["new_item"]=>"New Whistle"
  ["view_item"]=>"View Whistle"
  ["search_items"]=>"Search Whistles"
  ["not_found"]=>"No whistles found"
  ["not_found_in_trash"]=>"No whistles found in trash"
  ["parent_item_colon"]=>NULL
  ["all_items"]=>"Whistles"
  ["menu_name"]=>"Whistles"
  ["name_admin_bar"]=>"Whistle"
}

Therefore my question if anyone can help out, is how can I manipulate that object class in my function and pass the new one with the new labels back to the filter? Many thanks in advance.

https://ww.wp.xz.cn/plugins/whistles/