I have seen many of the same topics and everyone has a different way thay are asking.
your ship has a tab that is for visuals just add two more slots.
you would have to equip a weapon of your desired visual in it for it to apply.
so if my ship has standard phaser beams but i like to have the look of pulse phasers or kelvin phasers. i cant buy them on the exchange or enough to have a full set as long as i had one to put in the slot they would all look like pulse phasers.