We make thousands of factory built rods each year, but the many of our blanks go out to other rod builders to be built to a variety of different specifications as required by anglers. In the factory we can make slight alteration to the specification of rods specially ordered for customers. We can for example add the angler's name, or change the ring sizes and position. But we are not custom builders in the true sense, and if you want a rod tailored to your exact needs you have the choice of either building it yourself , or having it custom built by one of the many quality rod builders around. The custom rod builders have the time to talk through an anglers exact requirements, and can alter just about everything apart from the blank.
Handles are a good example.
You may require an oversize reel seat for a big reel, or you may wish to move the position if you have arms that are longer or shorter than average. Cork may put onto rod handles where Duplon is normally used. Ring spacing and ring size is something else that may be changed. Anglers from Continental Europe prefer higher stand off rings with double legs. UK anglers tend to prefers single leg rings.