Almost, not quite as simple as that. Since the introduction of SRS 2.2 there has been a bigger capacitor in the crash sensor, the idea being that in an accident there is a possibility of an open circuit of main battery feed so the capacitor takes over the deployment signal. Even earlier ones had a smaller capacitor so wise to let the system stand with the battery disconnected if your going that route for 30 min before working on the car. To be honest it makes little difference, never, ever turn the ignition on during the time the airbag module (or any SRS device) is disconnected and be aware that even static will deploy a bag, some don't believe it so I used to demonstrate this on SRS training courses at Volvo. Don't touch the contacts on either the bag unit or plug. We used to have 'test resistors' which were plugged into the harness the moment the bag was disconnected but with care you should be fine.
