The larger balls won't sit in the same position on the cone, so will only have an effect on the cup. In fact they could end up on the edge of the cone. They will also push the cone further out on the axle, which could cause problems with having enough axle protruding as well as more difficult mounting between dropouts. Finally, the larger balls will not fit into the groove already made by the smaller ones if it's a used bearing. If the bearings are in bad shape it's best to replace the part, with the exception noted by FB. If it's a new hub just ride it. If well adjusted the difference is not worth worrying about.