But speculation is half the fun! I'd hazard a guess that he would say that the owner of the plane should in fact be "free" to modify the control software of th

But speculation is half the fun! I'd hazard a guess that he would say that the owner of the plane should in fact be "free" to modify the control software of the plane, but that the owner (airline) would then be required to re-certify the plane as well. And that might mean that the Free argument extends to the airworthiness test suite used by the manufacturer as well.