WordPress at a glance
action is not described

woocommerce_product_type_changed action-hook . WC 1.0

Action for the transition.

Usage

add_action( 'woocommerce_product_type_changed', 'action_function_name_3', 10, 3 );
function action_function_name_3( $product, $old_type, $new_type ){
	// action...
}
$product
-
$old_type
-
$new_type
-

Where the hook is called

WC_Product_Data_Store_CPT::update_version_and_type()
woocommerce_product_type_changed
woocommerce/includes/data-stores/class-wc-product-data-store-cpt.php 863
do_action( 'woocommerce_product_type_changed', $product, $old_type, $new_type );

Where in WP core the hook is used WooCommerce

woocommerce/includes/class-wc-post-data.php 36
add_action( 'woocommerce_product_type_changed', array( __CLASS__, 'product_type_changed' ), 10, 3 );