An observer should not move anything in the path from the telescope to the wavefront sensor or the spectrograph. An exception may be a dichroic beamsplitter which could in principle be mounted before the first cube, because this will change the optical distance to the WFS and the slit with the same amount. If this distance is changed, then the WFS and the slit will have to be cofocused again. The cofocusing is crucial for getting spectra with high spatial resolution.
Do not move any parts of the spectrograph except the spectrum cameras. You may also adjust the slit plate rotation, the slit rotation, and the slit-jaws. Be very careful when working with these adjustments. Do not touch the reflecting slit plate.