Ok ac500u, I'll humour you one more time. We're talking about an airport with ATC, right? ATC control what is going on on the manoeuvring area, they know about everything that's going on. They'll tell you about anything that you need to know about based on what you are expected to do (or have been cleared to do).
In the hypothetical situation that I mentioned earlier - where the displaced threshold is so far down the runway that anything on the normal/take-off threshold is outside all of the obstaclre clearance surfaces and runway strip - I could, for example allow a vehicle to cross the normal threshold...and I may not bother telling you about it. I've cleared you to land and I'm going to assume that you'll aim to land past the displaced threshold because that's the bit of runway that's notified as available for landing. In strict terms, if you land short of the displaced threshold, it's little different to landing on another runway. You wouldn't land on a different runway to the one you're cleared to land on, would you? Even if you could see there was nothing else on the runway?
As to the NOTAM thing. I'm not going to NOTAM a runway crossing. And I'm not going to NOTAM that the approach lights will be u/s for half an hour on a glorious sunny afternoon whilst some maintenance is done. Why not? Because there's ATC and I'll tell you about it if you need to know - see above about basing what you need to know on what you've been cleared to do. If it was an uncontrolled field things would be different - stuff would have to be NOTAMed because it's possible that no-one at the field will be able to tell you about it. But we're talking about an airport with ATC.
You cite the warning in the Denham entry in the UK AIP. In the UK the AIP is an information publication (I guess the title gives it away a bit), airports can put pretty much anything relevant in their entry. It's probably there because some idiot chose to ignore the markings and caused a problem.
Airmanship or good aviation practise seems rarely to be explicit in law - it's very difficult to define anyway. In the UK there is legislation - ANO articles 63 and 64 - that says you mustn't endanger the aircraft or anyone else. It's a matter of interpretation as to whether any particular action constitutes endangering and definitive interpretation is the one decided in court. I would guess that many other states have something similar. If you want to try and avoid being accused of endangering I would suggest you follow the rules as the majority interpret them.
I'm afraid I tend to agree LanFranc both with the point he makes in his latest post and with the conclusion that your friend is clutching at staws and is going to have to accept that he may be wrong on this one - and, hopefully, before he does any real damage!