If you have to do it, do it well. Here are some tips for sweet substitutions.
This staple has no substitute.
Granulated sugar and molasses make a close approximation.
Because it contains cornstarch, powdered sugar should not be used for either brown or granulated sugar in most recipes.
To Replace: 1 cup powdered sugar
1 cup granulated + 1 teaspoon cornstarch ground together in blender (not food processor) Caution: This works very well for dusting over desserts, less so in icings or glazes.
Replacing some of the sugar in a recipe with honey, molasses, or maple syrup to add an extra dimension of flavor is a simple matter, provided you account for the extra moisture.
To Replace: sugar with liquid sweetener
Reduce liquid by 1/4 cup for each cup of liquid sweetener added
Caution: As liquid sweeteners vary in moisture content, acidity, and even sweetness, it is usually not a good idea to replace more than half of the sugar in a recipe with a liquid sweetener.