The end product is definitely much better than the script. However, the original ideas of the script - which I don't think Lynch had any real say in (though I could be wrong) - are largely unchanged. Coop enters the Lodge to save Annie, offers his soul to save her, then loses some of his courage, and pays the price. Also, the deal about Glastonbury Grove of the last episode is pretty nifty, and that was in the script. The main change, apart from toning down Windom's over-the-top character in the script, is the fact that it's in the Red Room. I think I'm leaning towards the idea that the Lodges (both Black and White) look the same to Laura, Leland and Dale, but might look different to another person, like Jeffries or Briggs. (Or it might just be that the White Lodge was supposed to be made of marble (to everyone) and have a throne for Briggsy until Lynch changed it, last-minute-style.)

It's definitely retcon. But good retcon.

"What credit card do you want to put that on?"
"Caash, prease."

When Coop investigates Dead Dog farm (ep19) the real estate agent tells him of the legend of the farm: "Of all the people in the world the best and worst are drawn to Dead Dog.. most turn away. Only the purest of heart can feel its pain. And somewhere in between, the rest of us struggle." This ties in with the other local legend (the one that Hawk tells Coop about in ep18): "My people believe that the White Lodge is a place where the spirits that rule man and nature here reside. There is also a legend of a place called the Black Lodge ... the shadow-self of the White Lodge. The legend says that every spirit must pass through there on the way to perfection. There, you will meet your own shadow-self... But it is said, if you confront the Black Lodge with imperfect courage, it will utterly annihilate your soul."

Together, these legends suggest the idea of the progression of the soul. Somewhere in the middle, most of us struggle, but probably through reincarnation, we have the chance to gradually increase the purity of our hearts (which could refer to pure good or evil). When one's heart is sufficiently pure, the BL is entered - if it is faced with perfect courage the soul may pass to perfection. If not, the soul is annihilated. Major Briggs and Earle have both been attracted to TP, though the purity in each of their hearts is very different.Major Briggs is being used by the WL spirits in an attempt to infiltrate the BL. They require someone exceptional, and with perfect courage so that they can enter without being annihilated. From time to time, Major Briggs is abducted by the WL Spirits. This is what happens when he disappears from the campsite with Coop (ep17). It has also happened many times before (as revealed by his wife in ep18). It seems that the Major is being sent into the BL, probably on a kind of fact-finding mission. When he returns, the WL spirits take his experiences from him to learn how they may enter the BL themselves -- leaving Major Briggs with no memory of what has happened.

Beware of BOB

When I call out no one can hear me,when I whisper he thinks the message is for him only..my little voice inside my throat,I always think there must be something that I've done or something I can do...But no one no one comes to help,he says,a little girl like you...

Well, it seems that Mike was originally from the BL, and was a killer, but then he saw the face of God and was purified, effectively "changing sides" from the BL to the WL, and when Cooper first encounters Mike, Mike is on the side of the WL, as it were.

In The Book of Revelation, a white (or pale) horse is indeed a symbol of death, as you say. "And I saw a pale horse, and its rider's name was Death, and Hades followed close behind him." Rev 6:7-8
 

Beware of BOB

When I call out no one can hear me,when I whisper he thinks the message is for him only..my little voice inside my throat,I always think there must be something that I've done or something I can do...But no one no one comes to help,he says,a little girl like you...