Great questions man. I'm looking forward to the answers as well, especially with your second question.

I don't know about the first 3 questions but #4 I want to point out that Stu Block from Iced Earth/Into Eternity does some black metal shrieks and death grunts while hitting very high falsetto notes without a vocal break nor without any change in his tone.

Dude, 3rd question is right on! I want to learn to scream the way they do it, that's my mission in life!

1) How do I practice everything? I mean, are there any scales or something? It's kinda weird doing it without scales

This is a totally new approach. It's not about scales, it's about experimentation. There are some scales for the warmups which you can use for the screams, but all in all, I wanted to make this all fun and give singers a break from scales.

2) Is there a better explanation beyond "aim for the palate and have good support"? I mean, maybe i'm just trying to make something simple to look harder than it really is, but I still did not really understand how to do most of the screams except for the pterodactyle one which I always kinda knew how to do.

It has to do with slight glottal closure. I believe I said, it's like grunting without grunting. Almost clench the voice like a grunt, but do NOT overexert it or else you'll strain. You MUST feel that grit sensation in the roof of the mouth. That is your guide to know you aren't over clenching in the throat.

3) Which one of the screams does the singers from Linkin Park and Avenged Sevenfold use? The dude who sings along with you on the long CD he's a good screamer, but his screams sounds NOTHING like LP or A7X, and i'm talking about the technique, not the timbre.

That was the company who put those names on there. I've told them to remove LP from Volume I promo. In fact, I believe in the last minute reading cards, several names were added for me to read that should have been saved for the other volumes. We will get to them, I promise. As for A7X, the only thing in this one that Matt does is the multi-tonal demonic sounding thing that he does t the beginning of Bat County.

4) Last question that I currently have: will screaming changeruin the voice? Let's take an extreme example to get a clear answer: let's say that James Labrie would take screaming lessons and learn to scream like the dude from the CD (Kelly?). Will it hurt his abilities to sing those high, clear and powerful notes? Will it change the tone of his voice? Will it make him sound fatigued?

NO, not if you do it right. If it is changing your tone, then you still need to work at it. The show I just did for National Geographic had film of me screamin, adding grit, hitting high notes, etc and there was absolutely no strain. However, they barely even showed ANY of that footage so I am trying now to get them to release some of that footage to me so i can add it to the members section. If not, I may have to film again hiring a doctor and film crew, BUT, it isn't fun to do, haha. Trying singing with something shoved up your nose and down your throat and you'll feel my pain;)

Is it possible to be a high pitched power metal singer and a grindcore screamer at the same time without sacrificing your abilities in each one of the singing styles?