Do the electrical codes have a solution to extend a cable that is short?
There are some splicing methods permitted inside walls, but ordinary wire nuts are not.
The usual solution is to use a junction box, with or without anything else in the box. For example, if your cable goes to a light fixture and you want to replace it with another light fixture a few feet away, connect the old &amp; new cables with wire nuts inside the existing box, cover it with a blank plate, and run the new cable to a new box where you want it. The cover plate has to be accessible, but it can be painted or wallpapered to match your wall or ceiling, or hidden behind a picture. It just needs to be accessible without any special tools (except a screwdriver to remove the usual two screws holding it onto the box).