If you see 19th century photographs of children with sharp looking hands, those lines have most likely been cleaned up with a knife on the neg.
Need to reduce a hotspot? One way to do this is to very carefully thin the overly dense spot on the neg with a knife blade. I've read that this was something everyone had to learn at Brooks at one time. Another approach is to sand the hotspot down with abrasive reducer--a product that Kodak used to make. I've managed to make it with brown tripoli abrasive and mineral oil.
Pinhole in the emulsion? Using a sharp stylus perpendicular to the base side of the neg, with the neg emulsion-side down on a lightbox, stipple the area over the pinhole to scatter the light when it passes through the base and it will blend in the pinhole.