srs module as in the controller? or one (or more) airbag? as far as the controller, i'm not sure if there is any manual that covers it (at least not bmw-specific). they are very particular about srs servicing. but as far as airbags, bentley may have it (sorry i only have bentley for 3 series).
but to answer your second question, about resetting, if you disconnect the battery and let the car fully discharge for about 20 min, it is possible you won't need a reset if you just swap airbags. as for the controller, i do not know.
The SRS controller unit can only be replaced by the dealer, it seems that the controller is coded and I have never come a cross a message that the code can be set.
So if you would replace the SRS controller it will not solve your problem.
P.S. check the following things before you start spending lots of dollars :thumbs
I have the same problem and the dealer did not fixed it. But I have found out through other forums that there can be a number of problem most related to wire problems.
1. check your ignition switch it wears out after 100000 kilometers. You can easy check the switch by giving a knock under the switch you will see that the airbag light turns on and off .
Also a symptom for wear on the ignition switch is that you can turn the key around in the ignition switch without anything happing. But a lot of electrical is triggered by the ignition key.
2. under you front seats there is a connector which connects the airbag sensors under the front seats to the control unit. The connector also wear out and the easy way is to short circuit the wires. The connectors can cause problems because the move when you adjust your seat.