In a 1 quart saucepan, stir gelatin with salt and 3 tablespoons sugar until well mixed. In a separate bowl, beat egg yolks with milk until thoroughly combined. Stir egg yolk mixture into gelatin mixture.
Cook mixture over medium-low heat, stirring constantly, until thick enough to coat the back of a spoon. Remove from heat and stir in rum and grated lemon rind. Refrigerate until cold but not firm, about 40 minutes.
In a large glass or metal bowl, beat egg whites until soft peaks form. Gradually sprinkle in 1/4 cup sugar, continuing to beat until whites form stiff peaks.
Remove gelatin mixture from refrigerator and gently fold into beaten whites along with the mixed diced candied fruit. Spread mixture into graham cracker crust. Refrigerate 1 hour or until set. Prepare whipped topping mix as directed on the package. Before serving, cover pie with whipped topping and sprinkle with candied pineapple.