Yes, you can substitute self-raising flour for baking powder, and vice versa, but it's important to keep in mind the differences between the two and make the appropriate adjustments to your recipe.
Self-raising flour is a combination of all-purpose flour and baking powder, which is a leavening agent. It is typically used in recipes that call for both flour and baking powder, as it provides the necessary leavening to help the baked goods rise.
If you don't have self-raising flour and need to substitute it with all-purpose flour and baking powder, you can use the following ratio: for every 1 cup (120 grams) of all-purpose flour, add 1 1/2 teaspoons (6 grams) of baking powder. Sift the flour and baking powder together to ensure they are evenly distributed before using them in your recipe.
On the other hand, if a recipe calls for baking powder and you only have self-raising flour, you can generally omit the baking powder from the recipe and use the self-raising flour instead. Keep in mind that self-raising flour already contains baking powder, so the leavening agent is already included. Adjustments to other ingredients, such as salt, might be necessary to maintain the overall balance of flavors.
It's important to note that these substitutions may not yield identical results to the original recipe, as the proportions of ingredients and the specific reactions they create can affect the texture and flavor of the final product. However, in many cases, these substitutions can work well as a viable alternative when necessary.