In practical terms, it's likely to be more rapid; and generally, the safety standards are at least as high - in fact, he may be horrified by some of what he finds (lack of an earth seems to be a common factor...)
The issue could be, getting someone to sign off work they haven't done. As he may himself feel, it's hard to put your name to something you haven't seen. So, if certification is going to be important (to increase your overall power rating beyond the level the supply company has on record as being appropriate; for licensing for alojamento local or other uses; for rental...) then you may want to bear that in mind, and perhaps link your son's work with a local electrician who is prepared to certify it.
As a point of reference, I have needed in the recent past to get certification for pre-existing but new wiring. I was quoted €1-2k, which was partly, I think, for the reputational risk to the person certifying. I am sure some would do it for much less! Not all electricians, or even qualified/registered ones, have the recognition to do formal certification, by the way. There's a kind of "self-certification of works" which is sometimes issued, but this doesn't count for power rating increases, or alojamento local, for instance.
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