First off, this only makes a superficial glimmer of sense if you have dropped collision coverage. You wouldn't consider this otherwise, I assume, but you didn't mention that.
I suppose if the vehicle is old and collision coverage has been dropped, you might save some money in a low speed collision with the air bags deactivated. A 2016 CX-5 GT AWD with a value in roughly the $10,000 - $20,000 US range depending on mileage wouldn't ordinarily go without collision coverage. Of course if you've got a couple of teenagers or had several claims already and your collision premium is through the roof and beyond affordability, I suppose you might take that risk. But would you want to deactivate the aribags if you're already in a high risk category? If you're just being a cheapskate then it looks like pennywise and pound foolish.
I suppose If you rammed something at 10 mph without incurring any liability loss and without the airbags deploying you might get away with $5,000 in repair costs. If the airbags deployed the vehicle would certainly be totaled. In fact, $30,000+ market value vehicles are almost certainly totaled after airbag deployment. You'd want to be wearing your shoulder harness of course so as not to bounce your head off the steering wheel.
But the circumstances where this would work out are very narrow. Sans collision coverage, the speed would have to be fast enough where the bags would have otherwise deploy but slow enough where the cost of repairs do not exceed the vehicles value. The risk/reward proposition does not look very good relative to the possibility of a higher speed accident where the airbags might save life or limb.
As to whether deactivating the airbags would void a liability-only coverage you'd have to take that up with the insurance carrier. I'm not sure why they would care. Whether the airbags deploy or not wouldn't make any difference in their claim payments to other parties.
