If I'm understanding your question correctly (how do I change some of the components of the entity and still know it's the same entity) the answer is that usual

If I'm understanding your question correctly (how do I change some of the components of the entity and still know it's the same entity) the answer is that usually in ECS entities have an ID assigned to them, so as long as the entity ID is the same it doesn't matter if the associated WeaponComponent records change.