Vedneros mentioned in my previous post

That's the spirit!!! And one thing about Warhammer 40K it is a HUGE place. So huge that there shouldn't be any certainity. You are talking about a million worlds here. And that is the estmated numbers just within the Imperium!!! There is no such thing as 'no it can't be done or no it can't happen' in a place so huge… There are things that are hard, really really hard and really really easy. But no impossibilities. Because of it's miniature nature every written canon fluff is so 'customizable' too (think about Imperial Guard, Space Marines, STC, Dark Age of Technology Government types of the planets, superstitous nature of the men(many have never seen a starship or possibility of void travel) and the most customizable thing the Warp). So you can play a Lord of the Rings, Fallout or a Star Wars… And you can play all of these in a single campaign! (i'm not recommending it though don't mess things too much ) Think freely and openly.. You will see that fluff of 40 k is very loosely tied and you can justify anything… (of course don't go out of bounds of common sense and grimdark )

You know the fluff of Warhammer 40000. So how much customization can be made to 40k without going out of fluff (talking about sectors, eldar craftworlds, tau septs, space marine chapters, death cults, IG regiments, titan legions and even sector based special organizations within the Imperium. Is it that possible to fit the 40 k to play any fantasy game like Vedneros mentioned (lets say can you play something similar to LoTR and still 40k ?) what do you think guys ?

It all really depends on the specific topic.

Take Space Marines for example; its highly unlikely there is a chapter of marines out there that entirely forsake the use of power armour, and instead use some sort of non-powered "super carapace" equivalent, and instead of bolters use "super lasguns." There is some consistency as to how the Imperium does things.

Lasguns in general are one of those things that often changes from world to world, but generally speaking, in DH, the lasguns listed beyond the core rulebook are the extreme outliers; the stock lasgun represents a fairly generic stat block that can cover a type of weapon manufactured on a million different worlds, as it is a highly standardized design.

Now on the types of worlds, certainly, it varies. Now, is there a world just like that of LOTR… difficult to say. Its been theorized that fantasy warhammer just takes place on some feudal world in 40k that the Imperium has yet to come into contact with (perhaps warp storms have kept it hidden). Realize that not every planet with humans on it inherently belongs to the Imperium of Man.

So yes, in theory there are alot of worlds out there in the 40k universe, the problem is, the further off the beaten path you go, the less the universe is going to look like 40k. At which point, why are you using these rules instead of another set of rules?

The main thing is to realize that any organization that reaches across "the entire" imperium (IG, Space Marines, Inquisition, Administratum, Arbites, etc.), are all going to have somewhat standardized methods. Arbites will have their black carapace armour (no not the implant), and have plenty of shotguns, IG will generally be armed with some sort of lasgun or autogun (not astartes grade boltguns).

If you mean with customization '' can i build my own chapters, IG regiments, death cults, arbites preceptory fortresses, even sectors'' yes you can of course do it, you can even create some weapons that special to your sector as well (think about calixis sector, its lathe blades and fractal blades are special to this sector) because of the game's miniature nature you can customize anything you like ( GW always encouraged it ) and yes you can create a sector and some 'local organizations' but dont go too far from the things that make 40k, 40k. Like Space Marines can use any weapon you may like but dont remove their Power Armour… Or as the Arbites not using a Black Carapace armour. You can stretch things anyway you seek proper but if you stretch things too radically you will distrupt the nature of the 40k. And about my LoTR example i guess you misunderstood what i meant, dont copy LoTR world but you can make a 40 k reflection of the LoTR if you want. You can use a Death Cult with sniper rifles but it will change the nature of ''fanatical zealot assasins'' instead you can do a local organization that trains assasins for example.

Problem is most of the fluff is extremely loosely connected… And thinking about the vastness and ''it varies from world to world, sector to sector'' concept of the Imperium and the galaxy it is really difficult to portray a 'default' for the setting…