Can I substitute buttermilk by curdling coconut milk with acid? I love to bake but can't justify buying buttermilk for the odd time a recipe calls for it.  Instead, I add vinegar to milk to replicate the buttermilk.(it works perfectly).  At the same time, I LOVE to bake with coconut milk, substituting it for milk in the recipe.  My question is, can I add vinegar to coconut milk and get the same results when substituting it for the buttermilk?
No, you cannot. Cow milk has proteins, which curdle when exposed to acid, thickening the whole thing. Coconut milk is simply a suspension of fat in water, with very few carbohydrates and practically no proteins. You cannot curdle it with acid.