Anytime the assembly line stops, it is a major (that is spelled EXPENSIVE) problem. That's why they don't do it. They are a very sophisticated manufacturer and could do it if it was in their best interest. Obviously they don't think it is.
This request isn't really like stopping the line in the middle to change something, it's taking the thing off the line at the end and onto a rack for stringing. The pups and electronics are the last thing to be put in/on other than the strings, no?

