If you still get the required intensity your results will (probably) be ok. The surface finish with the smaller shot will be rougher since the shot must go deeper into the surface. Note: for equal intensities with two shot sizes the dent diameters must be equal but the smaller shot will make a deeper dent. You should always check with the designer (or whomever owns the part) for permission to make a change in shot size, hardness etc. They may have had special reasons for their call-out of the S-460 shot or, maybe they don't care if you make a change.
