And where is that aeroclub, and that C42? If in Germany, yes of course, rules must be adhered to, and they are forbidden to be simple and straightforward. Otherwise, the mileage may vary, and there are lots of unknowns in today's Britain - as in tomorrow's, like as not.
@Fl1ingfrog above: I particularly like the "if any" bit - most appropriate
!
"Ultralight aircraft" is even a contradictio in terminis, strictly speaking: no aircraft can be an ultralight and no ultralight can be an aircraft. But I fully agree that switching sub-EASA craft between national registers can be difficult: my own pride and beauty took a full 3 months to pass from HU to BE. The key to success was that the type had been approved "as a type" by the BE CAA, but it took its time to convince the civil servants.
Also, may I be forgiven for suspecting certain manufacturers of earning money as they see opportunity, for example by requiring strengthened landing gear. For one example, I see the Eurofox
https://en.wikipedia.org/wiki/Aeropro_Eurofox being marketed as a 1200 lbs LSA in the USA, with no mention of technical differences with the European ultralight version of 450/472,5 kg MTOW.
Meaning that this Eurofox can obviously be operated at 600 kg with no modifications. There can of course be other manufacturers who started out with a less sturdy construction.