Just need a bit of clarification

Hey fellow xenos haters! Just looking at the deathwatch terminator squad, with it saying 3 models can swap for heavy weapons (missiles/assualt/plasma) could you technically take a 5 man squad with three missile launchers then have TH/SS on the other two for some extra punch in melee?

If so what do you think about two termies teams loaded with missiles and two Proteus team loaded with triple missiles on the terminators? The missile racks terminators are some of my favorite models so I'm contemplating cramming a bunch in a list.