When handling airbag modules (steering, glovebox, seat or curtain) the technician uses a 'test' resistor that matches the resistance of the airbag igniter. The procedure is to disconnect the battery, wait 30 seconds for the internal (in the crash sensor) capacitor to discharge, if your smart you give it a couple of minutes just in case, and unplug the connector and fit the test resister to it. The airbag can then be removed, of course you don't go sticking your fingers on the connector pins as even static can cause them to deploy! Provided you follow procedure the warning light should not come on, if it does its just a case of 'Read the Code - Clear the Code' in the same way as OBD2 codes.
