Yes vitamin C can prolongate the shelf life more or less up to a month in a good storage condition in a sterilized airtight container and in the fridge. It’s not the strongest preservation method you can find. For external use the risk is very minimal but if it’s for eating, we’d recommend sticking to fresh aloe if possible. Also that if you add vitamin C, you then need to consider that in your nutrient intake when consuming it. If it’s for external use, you can add some potassium sorbate to preserve it up to 1 year or opt for the freezing method