Adding dairy to non-perishable sauce

Each of the parts of your current recipe can be kept for months in a closed container, but once the container has been opened, you run a risk of spoilage.

Mixing two or more ingredients increases the risk of something going wrong, as with the ingredients you mix air and possible contaminations into the sauce.

You can mix a sauce like this for use that same day, maybe the next but should not store it for longer.

Adding a 'non shelf stable' ingredient will increase the risk for something going wrong by a lot. When you mix the yogurt into the mix you should use it within a few hours, even when you store it in the fridge. (It is not guarantied things do go wrong but the risk goes up again against the mix without yogurt.) Likely it will be alright for a few days but you better mix just before use and not store for later.

The pH value does help keeping bad things from happening but it can only go so far. When mold spores get in, they can develop into full scale molds. And that is just one thing going wrong.