LotR -- Book 6 - Chapter 3 - Mount Doom

[Kuruharan]

Could He not have shown Himself in all His glory to the Numenoreans & intimidated them into returning to Numenor?

Honestly, I doubt this would have done any good. They were hardened Morgoth worshipers by that point. They would probably have seen a manifestation of Eru as something to try and fight against. The last test of their god before he rewarded them with immortality and new worlds to conquer.

Yes, because Death was not a punishment, but an entirely natural thing (even unnatural deaths - as a result of violence, disease, suicide, etc could come under the heading of 'natural' as they are a consequence of events happening within the created world. We could even say that deaths caused by the Valar are 'natural' because once they entered into Arda they became a part of its nature, unable to leave it of their own accord).

With Gollum (& the Numenoreans) it is a case of unnatural (ie supernatural) death, because the cause of their death is brought about from beyond the Circles of the World. It is a Divine intervention which causes them to die, a breaking in of the supernatural into nature.

(There seems to be something of a wall here.)

Let's try look at this from Eru's perspective (again). As I said above, "death" is not an ending for him. (Actually it is not an ending for anybody.) The end for mortals is the same. He knows where to find them.

In both of these cases Eru acts at the last to defend the creation from the massive havoc and/or domination of rogue, misguided elements that have revolted from him. He has given everybody involved plenty of opportunity to turn from their wicked ways and delivered warnings to that end. Would you prefer that he just stay out of it?

Do you not think that Eru has the right (some might say responsibility) to intervene in his own creation? He made it, after all. It would not exist without him. There is ultimately some sort of plan at work for how he wants it to turn out in the end.

I don't think that any activities he undertakes like this could be considered as having two moral codes, but rather different roles within one code (remembering that the moral code is part of Eru.)