Engine starting batteries---typically---also feed the base vehicle's electrical system---air bag's are part of that system, fed by the starting battery so yes that needs disconnected.
If your SMB's battery system(s) have been modified from its original form as delivered from the factory I'm not sure what steps are necessary to completely disconnect power to the chassis wiring.
Testing windows, headlights etc etc should be a reliable indicator if power has been temporarily removed.
I will say but DO NOT ADVISE most times replacing a clock spring doesn't trigger the SRS but that's more "dumb luck" than anything else. Air bags unexpectedly deployed when occupants aren't seated normally can and will cause bodily injury. They WILL leave a mark!
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