Absolutely! One of the great features of this apple walnut muffin recipe is its versatility. If you're looking for substitutions, you can use whole wheat flour instead of all-purpose flour for a healthier alternative, which will also lend a nutty flavor to the muffins. For sugar substitutes, honey or maple syrup can replace granulated sugar; however, you may need to adjust the liquid ingredients slightly. If you prefer not to use walnuts, you can use almonds, pecans, or even omit the nuts entirely for a nut-free option. Additionally, if you want a dairy-free version, you can replace the Greek yogurt with a plant-based yogurt. These adjustments can cater to various dietary restrictions while still delivering delicious muffins.