First thing first: as long as these substances are just dissolved speaking of their identities doesn't make much sense. They dissociate, so the solution doesn't contain salts per se, just ions.
Solution prepared by dissolving sodium chloride and potassium iodide is identical to the solution prepared by dissolving sodium iodide and potassium chloride (assuming you paid attention to concentrations). It contains Na+, K+, Cl- and I-. That's exactly the same type of situation.
If you evaporate the solution to crash out salts, they can precipitate in some specific order, which can be to some extent equivalent to doing the metathesis reaction.