Hi,
I’m not really sure what is MPN, but there is a universal [alg_product_meta] shortcode, that can get any data saved in product, e.g.:
[alg_product_meta name="_some_meta_id"]
You should change _some_meta_id to meta name that “Cart Product Feed Additional Product Fields” plugin creates.
Hope I made it little more clear, and please let me know if you have any more questions.
Best regards,
Tom