Prepare cake mix and bake according to package directions using two 9-inch round cake pans. Cool in pans on wire racks 15 minutes. Remove cakes from pans; cool completely.
For rum filling, combine all ingredients in small bowl until well blended. Cover with plastic wrap; refrigerate until ready to use.
For whipped topping, place 2 cups whipping cream in large bowl; beat 1 1/2 to 2 minutes or until soft peaks form. Add powdered sugar and vanilla; beat 20 seconds or until stiff peaks form. Cover with plastic wrap; refrigerate until ready to use.
Place pineapple cut side down on cutting board; slice very thinlyl Place slices on paper towels; pat dry.
Place 1 cake layer on serving plate. Spread half of run filling evenly over cake. Spread 1 cup whipped topping evenly over cake. Sprinkle with 1 cup coconut; top with remaining cake layer. Spread remaining rum filling evenly over cake. Spread remaining whipped topping evenly over top and side of cake; sprinkle top with remaining coconut.
Press pineapple slices around side of cake vertically, overlapping slightly. Reserve any remaining pineapple slices for another use. Refrigerate cake until ready to serve.