I've never attempted to change the crank sensor with the timing belt on, but I'm sure others have, and will chime in with more direct experiential answers...
Now, my first reaction was: Nope, you gotta take the timing belt off, because the crank timing sprocket has to come off to get the crank sensor out.
However, I just went out and looked at my spare engine, and it looks like, if you were really clever and dexterous, you
might be able to get the sensor out with the belt and sprocket in place. You'd have to make sure the crank is rotated so the shutter window is aligned with the sensor, otherwise you definitely won't be able to get the sensor out.
With my engine on a stand, out of the car, it looks like I could probably get the sensor out with the timing belt on, but you're gonna have even more trouble doing it in the car.
All said, there's only one way to know for sure!
Regards,
Jon Heese