It wouldn't seem likely just due to the weight which should remain consistent particularly with a non-wooden ramrod. But anything else that might affect the barrel vibrations could.I agree with your statement and might add that anything added or taken away will effect how a rifle performs.If you can't take something away you can cancel it out by adding weight to the barrel. A thick heavy barrel is used in target rifles because of this very thing. Muzzle loading rifles by their nature are heavy barreled therefore It is logical to think that something the weight of a ram rod should make little difference to the accuracy of the rifle? Am I right? I don't know but I don't worry about the weight of a ram rod when I am shooting>
Right off the top of my head, I can't recall the optimum spot in the barrel harmonics (whip) the projectile should leave the muzzle.
Most important, it's consistent from shot to shot. Whether 5 minutes or 5 days between shots. Anything that changes that should have an effect, even if it still performs to our satisfaction. A number of factors affecting internal ballistics.