There is different dies and taps for cutting or chasing threads, using a chasing die to cut threads will make a mess of the die and the forks, make sure you have the right one. As long as you use the right tools and techniques, and the forks are suitable then there is no problem cutting threads on it. If your in doubt either get new forks or get Mercian to do it, they will have done it before loads of times.
There is different dies and taps for cutting or chasing threads, using a chasing die to cut threads will make a mess of the die and the forks, make sure you have the right one. As long as you use the right tools and techniques, and the forks are suitable then there is no problem cutting threads on it. If your in doubt either get new forks or get Mercian to do it, they will have done it before loads of times.