How long do you plan on bottle aging? If it were me, i wouldn't. You should be okay. 2 doses in just 4 months is quite a bit IMO. Maybe just a tiny bit....1/8 tsp or even less.....if anything.
Not knowing pH, but assuming that since it is a kit around 3.5 pH. You should be at 30-40 ppm. If you added 50ppm on 12/3, in a topped and well sealed carboy, chances are you are in the 20's. I would go with a 1/2 dose, .8 grams of SO2 as well.