Not really. Keep in mind the GI is based on 50g of carbs from a given food/mixture. If you take a carb with a GI of 30 and a carb with a GI of 100 and mix them in equal shares, the GI of the final mixture would be around 65. By adding the milk you are adding to what already exists, but are not removing the insulin response or raise in blood sugar of what is already there. Whole milk might be an except and fat can slighly reduce the absorbsion rate of a carb, thus lowing the GI, but you are not going to turn a high GI carb into a low one simply by adding fat to it.