mooska

In the meantime, I did make it with filters. Leaving it in case someone looks for solution.

function bc_threewp_broadcast_broadcasting_before_restore_current_blog( $action )
{
	$bcd = $action->broadcasting_data;  // Convenience.
	
	$cf = $bcd->custom_fields(); // Convenience.
	
	// Load the current fields.
	$child_fields = $bcd->custom_fields()->child_fields();
	$child_fields->load();
	
	// And now go through them, processing only arrays.
	foreach( $child_fields as $custom_field => $values )
	{
		$value = reset( $values );
		
		$array = maybe_unserialize( $value );
		
		// We are only interested in arrays.
		if ( ! is_array( $array ) )
			continue;
		
		$type = '_bto_data';
		
		if( $custom_field == $type && $array) {
			foreach( $array as $index=>$id ) {
				foreach( $id['assigned_ids'] as $inner_index=>$assigned_id ) {
					$converted_value  = ThreeWP_Broadcast()->get_post_broadcast_data( $bcd->parent_blog_id, $assigned_id );
					if( $converted_value ) {
						$child = $converted_value->get_linked_child_on_this_blog();
						
						if( $child ) {
							$array[$index]['assigned_ids'][$inner_index]  = $child;
						}
					} else {
						//
					}
				}
			}
			
			$bcd->custom_fields()->child_fields()->update_meta( $custom_field, $array );
		}
		
	}
}

add_action( 'threewp_broadcast_broadcasting_before_restore_current_blog', 'bc_threewp_broadcast_broadcasting_before_restore_current_blog' );

Its official WC package:
https://woocommerce.com/products/composite-products/

The structure is pretty simple (its a private fields, so the meta name is _bto_data):

[bto_data] => Array
(
[0] => Array
(
[group_id] => 1556369804
[title] => Straps
[position] => 0
[description] =>
[thumbnail_id] =>
[query_type] => product_ids
[assigned_ids] => Array
(
[0] => 794419
)

[default_id_categories] => 794419
[default_id_products] => 794419
[selection_mode] => dropdowns
[pagination_style] => classic
[quantity_min] => 1
[quantity_max] => 1
[discount] =>
[display_prices] => absolute
[show_product_title] => 1
[show_product_description] => 1
[show_product_thumbnail] => 1
[show_product_price] => 1
[show_subtotal_product] => 1
[show_subtotal_cart] => 1
[show_subtotal_orders] => 1
)
)

In here its a single component (one element array) and product id is: 794419, so that should be straightforward. There can be several of those components. Im fighting with filters atm, but getting that first hand would be much appreciated.