Step 1: Preheat oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan.
Step 2: Prepare cake mix according to package directions. Pour batter into the prepared pan.
Step 3: Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean. Remove from oven and let cool in the pan on a wire rack for 10-15 minutes.
Step 4: While the cake is still warm, use the handle of a wooden spoon or a fork to poke holes evenly over the entire surface of the cake, about 1 inch apart.
Step 5: In a medium bowl, whisk together the cream of coconut, pineapple juice, and light rum (if using).
Step 6: Slowly and evenly pour the cream of coconut mixture over the warm, poked cake, ensuring the liquid seeps into all the holes.
Step 7: Cover the cake with plastic wrap and refrigerate for at least 2 hours, or preferably overnight, allowing the cake to fully absorb the liquid and chill completely.
Step 8: If using, toast shredded coconut in a dry skillet over medium-low heat for 3-5 minutes, stirring frequently, until golden brown. Let cool completely.
Step 9: In a large bowl, gently fold the well-drained crushed pineapple into the thawed whipped topping until just combined.
Step 10: Spread the whipped topping and pineapple mixture evenly over the chilled cake.
Step 11: Garnish with toasted shredded coconut and maraschino cherries, if desired. Keep refrigerated until serving.