Would freezing a whole pineapple change it visually?
Assuming you are displaying the whole pineapple, then you don't need to freeze it. Pineapples will maintain their appearance for quite a long time which is why they were able to be shipped around the world during the age of sail.

To help it keep a bit longer, each day stand the pineapple up on end and drizzle water into the leaf crown. This is how this plant gets most of it water and nutrients and it will help keep the fruit hydrated for a little longer than ordinary.