1. Place chocolate chips in small microwave-safe bowl. Microwave at MEDIUM (50%) 1 minute; stir. If necessary, microwave at MEDIUM an additional 15 seconds at a time, stirring after each heating, until chips are melted. Stir in rum and corn syrup.
2. Stir together vanilla wafer crumbs, pecans, and 1/2 cup powdered sugar. Drizzle chocolate mixture over crumb mixture, stirring until well blended. Shape mixture into 1-inch balls; roll in powdered sugar. If desired, place cherry half in center of each cookie, pressing down lightly.
3. Store in airtight container several days to develop flavor. Before serving, roll balls in additional powdered sugar, if desired. About 4 dozen cookies.