Okie, even if there was not an already reasonable legal way for CASA to do what they did, the government could simple pass a statutory law approving the past actions. This has been done before, and as long as the law is within the executive powers of the crown then there is no issue with using this course of action. This is what was done during the Tampa crisis.
Of course someone could try to challenging this action, but considering the power of licensing is well within the executive power of the crown, and that the public interest in the safety and abilities of a pilot well outweighs the small intrusion, the case would not see the light of day.