Well, you could. But the end product would be quite different, without the crunch of corn flour (corn meal.)
I personally would use normal cornflour instead because wheaten cornflour is really hard to find but you may wish to use something else.
Much like how flour is used in gravy, cornflour is a thickener. If the cornflour is omitted from the recipe, the pie filling will come out with a somewhat soupy texture.
cornflour and water, food coloring is optional
Yes, we can substitute buttermilk for milk in recipe.
The only alternative to cornflour I know is to mix equal parts of softened butter and plain flour to form a paste and use the paste instead of cornflour.
It's called cornflour in the UK too. It's flour made from maize and has a yellowish colour. You should be able to buy it from any supermarket.
margarine
vinegar
cream cheese
If you want, you can substitute chicken thighs for turkey thighs in a recipe. It will give your recipe a different taste.
Recipes calling for rice, you may substitute with ouzo with you have no rice.
You can, but it would no longer be a vegan recipe.