Simply using the switch does not give a sensible answer. When DE perturbations are turned off and w!=-1, I see large changes to the small scale power where there should be none.Why put people off about changing it or keep it highly depricated ?
As Antony says, if you use the switch, you MUST ALSO edit the equations somehow. CAMB should at least come with this warning.
The switch might also come with armed guards and require two high-ranking officials to enter launch codes and turn two separate keys simultaneously, but that's probably too much.