Hello !
"Does anyone knwo how those new adt stuff work? Like what is the _obj0 or _tex0 files used for and more important how do i pack a patch that ahs the highest priority in laoding?"
Adt is separated into 3 files, adt (main), _obj (M2 and WMO informations) and _tex (Textures informations) each files contains chunk (essentially old chunks)
Like this :
http://mjollna.org/docs/adt.png"I treid edding the old patches overwriting a existing adt in Kalimdor but it dint changed at all. At one point in my tries my client told me hes downloading new content 
with the ingame downlaoder.
Here we go with the next Question: Does anyone have experience with this downloader and knows ho to prevent him from overwriting the edited adts?"
For cataclysm modding, you should use a special wow.exe, without the Mfil verification and others protection
You can find a modified wow.exe on Ownedcore.
But ! You must have your game 100% downloaded
You can see that in the mainmenu, the computer screen icon.
"If anyone managed to acually get a custom adt working in Cata client please let me know. "
It's difficult !
Some ADTs work, but you can't touch (this) Azeroth and Kalimdor, Cmapchunkalphashadowbits error, somethings with the flags in the WDT, i don't know how to fix this.
But you can create a new map.
Raising terrain, Smooth operation, Placing M2, Add Water, Area flags and texture work
But, if you clear texture from your adt, you will get many wow errors, so never delete texture from your adt, you can swap them.
And there is a collision problem when you spawn WMO, you must use Noggit unstable version for fix this (saves your adt with sdl 1.3 then open unstable noggit and resave yours adt)
Edit :
For creating Patch, The names of the MPQ are : wow-update-base-XXXXX
Cata 4.3.4 rev 15595, you must choose value greater than 15596.
You should use a special Wow.exe for this.
