In an airtight plastic container, combine pineapple, coconut cream, simple syrup, and ¾ ounce lime juice, and transfer to freezer until frozen, at least 1 hour (the sugar in the mixture may prevent it from freezing solid; this is okay).
In a blender, combine frozen pineapple mixture with ice-cold rum and ice and blend until thick and slushy. Taste, then blend in the remaining ¼ ounce lime juice, if desired. Pour into a large glass, garnish with pineapple and/or a cherry, and serve, with or without a paper umbrella and straw.
If you want to make multiple drinks, you can pre-batch up to a double recipe (a blender may not hold much more than that easily) in a single container, then divide after blending; for more than 2 drinks, use separate containers to hold more servings.
