The changes I've made to the recipe:
1/3 cup of butter instead of 1 cup of margerine
add 1/2 cup applesauce (sweetened)
3/4 cup of sugar instead of 1 1/4 cup
sprinkle top of muffins with turbinado sugar before baking
I don't have a recipe but I often substitute fat free plain yogurt in baking recipes. I sub some/all of the oil and liquid. You have to be careful as muffins are supposed to be moist but Yogurt really does add moisture and a soft crumb texture. I have done this for banana bread recipes and other types of sweet breads with great results. I use very little oil or butter in my baking to save calories. Besides, has anyone bought cooking oil lately? I can't believe how high it is now. Sorry kids, you can't go to college cause mommy has to spend your fund on groceries. Sheesh.