Nutsplats

I have an 09 ES 350 and my airbag light is on. After some time I'm pretty sure I've narrowed it down to the Occupant Classification ECU. First question is can I get away with buying a used one or do I have to buy new ? It shouldn't be too hard to replace. Remove the front passenger seat and it's underneath. Next question is if I replace the Occupant Classification ECU what do I need to do to program it to the VIN and the car. Lastly is there anything else I'm missing or any other information I need to know before I do this.
Thanks.