Is there a way to safely disconnect the main airbag without disc the 12v battery?

There might be, if you look in the wiring diagram and find all the fuses for circuits (there might be more than one) powering the airbag system, and you pull all of those (and then wait the prescribed amount of time before working on any airbags, just as if you had disconnected the battery).

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I haven't looked, but you might end up finding some of the same circuits that power the airbag system also power the other ECUs whose settings you want to retain, so you may or may not be able to accomplish what you want.

 

The other issue you'll probably run into is SRS / air bag system faults that may or may not reset. Do you have techstream or a good diagnostic tool that can reset them? Personally, I never touch air bag systems with the 12v battery connected. It's a self-preservation instinct after having seen a few activated for fun. Gotta be careful with that stuff, some models have internal inertia activation mechanisms, not just impact sensors in the car body.

from the repair manual:
Before starting work, wait at least 90 seconds after the
power switch is turned OFF and after the cable of the
negative (-) battery terminal is disconnected. (SRS
parts are equipped with a back-up power source. If
work is started within 90 seconds of turning the power
switch OFF and disconnecting the cable from the
negative (-) battery terminal, SRS parts may deploy.)
(The SRS is equipped with a back-up power source, so
if work is started within 90 seconds of disconnecting
the negative (-) terminal cable of the battery, the SRS
may be deployed).

That being said, the repair manual also explains a method of engaging a "deactivation", but is for troubleshooting only. Be safe and disconnect the 12v battery.

 

I'd take the 12 volt battery disconnect ramifications, however remote, over the potential for airbag explosion, any day.