I had some spokes cut and re-threaded at an LBS and it was a disaster. Apparently they had a Phil Wood machine but no one really knew how the use it. The first 36 15g spokes were to be cut by about 5mm, but the operator used a 14g die so the the threads were barely there (they eventually replaced these with new spokes, but not until I returned them). The next 36 spokes were 2 mm apart and 18 needed to have the previous threads picked up; they used the right die, but the threads varied in length, so it was a real chore to even up the tension from the start.This may not be the norm but keep in mind what you are asking is outside the norm of some LBS.