Yes sensor can be removed without removing the hub. Jack the car up, remove the wheel, undo the screw with a 5mm allen key. Spend the next hour trying to get the old sensor out! and then refit the new one.
If the sensor wont come out easily, which i'd be very suprised if it did, the only way I have found to get them out is to remove the screw, then use a chisel to break the sensor in half. Pull out the all the wiring from inside the sensor which is a lot of thin copper wiring, then using a thin screw driver gently tap the head of the screw driver inbetween the plastic sensor casing and the hub. It should at some stage crack the casing and then it will easily to pull the rest. Once done, clean the inside of the hub hole and refit the new sensor. It's a little bit rough and ready way of doing it but it works and as long as you are careful wont damage
