Wait, what?! Damn, there goes that plan.
Seriously though, I know. On my 182 I fitted a decat, which caused the engine light to come on, even when the original cat went back in, it remained. I never got round to it, but I was told it just needed turning off and because the original cat was back in, it wouldn't return.
I think the previous owner had a decat at some point, so for now the plan was to knock the engine light off and see if it comes back.
The airbag light is almost certainly because there's been some dodgy wiring done under the seat, by someone before I owned the car. Again, the plan was to fix the wiring, knock off the lights and see if they come back, as part of the diagnostic process.
Shame I can't just wave a wand at it though...