The problem with CASA, as demonstrated by this debate, is that they rely on legal arguments which by definition, have nothing to do with safety, in fact the legal arguments are anti safety.
Hence Djplls observation that as his Decathlon has no performance charts, he can do what he likes in respect of temperature with no possibility of CASA prosecution.
In other words, the absence of information on the performance degradation at high density altitudes in the documentation is a net positive from the point of view of avoiding prosecution. This is the reverse of a safety culture.
I have noticed this before in the way aviation is regulated, for example, my aircraft, if it is ever finished, needs an environmental noise compliance certificate ...which will state that this aircraft is exempt from the requirement to have a compliance certificate!
From the point of view of creating a safety culture, it appears to me that CASAs approach is counterproductive. For example, I now know enough to ensure that I will never fit a camera or post stuff to youtube. Data logging is going to be disabled, the maintenance manuals and POH I need to produce will be the bare minimum skeletons I can get away with and any aviation activities will be conducted as far from prying eyes as possible. The aircraft will never fly to shows or events which attract CASA ramp checkers.
Basically CASA has so prescribed aviation activities in this country as to almost make it not worth it.