Don't really see it as injustice, the rules are clear and you have a copy and agree to them when booking your test, your car was not road worthy and would also fail an MOT with airbag light flashing, no idea why you'd choose to make the car less safe.
However, there are a couple of screws for the steering cowl, and a couple underneath for the dash surround, (lowering the steering wheel if possible will give a bit more room).
Once this is removed, then you can remove the screws for the dash cluster, remove cables, connectors and speedo cable, then you can remove the light for the airbag, then fitting is just the reverse.
