In restoring a piano, restringing is normal. Restringing can also be done without a complete restoration. Old pianos, especially uprights, frequently have bass strings that are “dead”. The sound is tubby, unfocused, weak. Some strings were wound with a material other than the standard copper. A new set of bass strings makes an amazing improvement.
Part of installing new bass strings is rescaling. This means calculating new manufacturing measurements. Before the advent of computers, core wire sizes and wrap sizes were a rather hit-or-miss guess. Now, with the help of computers to do the complicated calculations, the impedance, inharmonicity, string contact time, and several other factors, can be calculated for the best tone and tunability for a set of bass strings. This is always done in my shop.