I've frozen raw peppers before. Chopped, they freeze well. Whole, they thaw all wrinkly. I've never frozen cooked pepper though.
What did you stuff them with? I would put them in the fridge and eat them tomorrow, just to be safe.
They are stuffed with cooked ground beef, spinach, parmesan, bread soaked in milk and a homemade tomato sauce. I will eat some today but between the two of us we only eat one at a time served with rice. So I don't want it for four meals in a row!