RESERVE 24 candies for later use. Place remaining candies in large freezer-weight resealable plastic bag; freeze 1 hour.
MEANWHILE, grate enough peel, then squeeze juice from 2 limes to measure 2 Tbsp. EACH zest and juice. Cut remaining lime into 6 slices, then cut each slice into quarters.
HEAT oven to 350°F.
CRUSH frozen candies. Prepare cake batter as directed on package; stir in 3/4 cup crushed candies, and 1 Tbsp. EACH lime zest and juice. Spoon into 24 paper-lined muffin pan caps. Return remaining crushed candies to freezer.
BAKE cupcakes 18 to 20 min. or until toothpick inserted in centers comes out clean. Cool cupcakes in pans 10 min. Remove from pans; cool completely.
BEAT butter in large bowl with mixer until creamy. Gradually add sugar, mixing well. Blend in milk, 1 Tbsp. at a time, until frosting is of desired spreading consistency. Beat in vanilla, then remaining lime zest and juice until blended.
SPREAD frosting onto cupcakes; sprinkle with remaining frozen crushed candies. Top with whole candies and lime slices.
Recipe Tip: How to Crush the Frozen Candies Use a meat mallet or the bottom of a heavy skillet to crush the frozen candies while still in the bag. If crushed candies stick together, lightly tap bag on counter-top to separate the candy pieces before using as directed.