A customer has a high-end range hood with a variable speed motor. The controls for the fan and lights are difficult for his wife and daughter to reach, so he wants to add a speed control on the wall. The controls for the existing fan are electronic, and I don't believe that putting a fan control ahead of them (or after them)is a good idea. It would be (2) controllers wired in series.
If this is a brand new install or the hood still has a factory warranty on it I would not touch it either.. If the hood is out of factory warranty or it was for myself say, I would bypass the existing controls for both the light and fan, and then use a standard speed control for the fan and a separate switch or even a dimmer for the light.
