Electro - Add Accessories Export & Import Support in WC CSV

functions.php

if( ! function_exists( 'electro_child_add_accessories_export_support' ) ) {
    function electro_child_add_accessories_export_support( $meta_value, $meta, $product, $row ) {
        if( isset( $meta->key ) && ( $meta->key === '_accessory_ids' ) ) {
            $meta_value = implode( ',', $meta_value );
        }

        return $meta_value;
    }
}

add_filter( 'woocommerce_product_export_meta_value', 'electro_child_add_accessories_export_support', 10, 4 );

if( ! function_exists( 'electro_child_add_accessories_import_support' ) ) {
    function electro_child_add_accessories_import_support( $data ) {
        if( isset( $data['meta:_accessory_ids'] ) && ! empty( $data['meta:_accessory_ids'] ) ) {
            $data['meta:_accessory_ids'] = explode( ',', $data['meta:_accessory_ids'] );
        }

        return $data;
    }
}

add_filter( 'woocommerce_product_importer_pre_expand_data', 'electro_child_add_accessories_import_support' );