Let me stop you right there. You sure can. Pretty much any substitutions or additions you'd like to make will be just fine in a recipe like this. Some easy options are changing up the greens, beans, or dressing (search this site for more great options), adding a grain, or adding a crunchy topping like nuts or seeds. I recommend keeping a wide variety of colors, textures, and flavors, and I like to include a leafy element, a starch, and some crunch whenever possible.