Does eating pineapple sweeten the taste of semen?

In short yes and no. The food you eat does directly affect any taste associated with semen. People who eat more fruits and veggies will have a sweeter taste while people who eat more meat will have a bitter taste. The exception is asparagus. This veggie will result in a very unpleasant taste.

However, to change your taste you must eat a consistent diet. Just eating some pineapple will have little effect on the taste.