you mean replacing the sensor?
well if he is replacing it, it doesn't matter if he is careful with it or not.
Worst thing that can happen is you jack up the threads in the exhaust, then you can't put a new one in.
Do drive the car and take it out hot or heat it with a torch. Much much easier.
And make sure you have the right sensor, you should be throwing a code and that code will point you to which O2 sensor it is.
And everything I just wrote I've had the pleasure of learning the hard way.
Good luck. If no problems, it's a ten minute fix.
Gmac