Well, I was hoping for a “yes, redirecting the trolley is intrinsically evil”, or “no, it isn’t”. The only way the action of throwing the switch can be immoral - given that the intent is to save the four - is if throwing the switch - which redirects the trolley at an innocent person - is an inherently evil act. Would you agree with that?
I think I can show that it is not inherently evil by changing the conditions slightly. Suppose the track after the switch is a circle, and the switch only determines whether the trolley goes around clockwise or counterclockwise. When the trolley completes the loop it simply heads back out the way it came.
The switch is set to send the trolley around to the right - counterclockwise. One third of the way around the track in that direction an infant’s mother is caught on the track. One third of the way around in the other direction a car is stopped on the track, with the woman’s infant child inside. When the trolley hits the car it will derail.
So, if the trolley continues around as the switch is set, it will first strike and kill the mother, and continue on until it hits the car, killing the infant, derailing and stopping. If, however, the switch is thrown, the trolley will go around clockwise and strike the car first. Again, the child will be killed, but the car will derail the trolley and the mother will be saved.
If your position that directing the trolley at an innocent person is an intrinsically evil act, then you must let both the mother and the child die, but if you take that stance then I see no way for you to reconcile the doctor’s action that saves the mother yet causes the child to die. I don’t think you can allow the operation but disallow the switching, yet if you allow the switch to be thrown in this case you must also acknowledge that redirecting a trolley at an innocent person is not intrinsically evil, in which case you must also allow it to be thrown to save the four.