It will be interesting to simply swap them out rather than keep three of the same weapon. While there aren’t a lot of weapon mods present in Destiny 2’s beta, you can check out three types: These appear to have control over a weapon’s power, Burn, and even appearance (sort of how like Ornaments worked in Destiny 1).
During the beta, you can see that there is a new section when checking out a firearm called Weapon Mods. Destiny 2 is changing things up quite a bit over the first game, and that includes how players approach weapons.