How about chalking down the extra MAD-OPO segment to some more tier points/miles/loyalty points and redeem a flight from OPO to VGO where you wanted to go to instead? That way you’ll fly two extra segments but you don’t risk losing the whole transatlantic ticket.

Example redemptions are available using AA miles for only 12.5k miles and $42 for an OPO-MAD-VGO trip (obviously don’t know what date you need)