The same question: Would a custom blizzard.j in a map work 100% allright ?

I am starting to think that the only hope for my map is to edit blizzard.j directly, but I once heard that desyncs, anyone knows if it is still true? (after the patches)

Why you want to edit the blizzard.j???
You can just rescript the functions with no desyncs and add them to the map... the blizzard.j file is a bit heavy to be added to the map and if wc3 gets updated the new blizzard.j of the new patch will not be used for your map.

No, it did never desync. The only issue was that it wouldn't load under certain conditions. (i think if you played another map before and then started your map)

AIAndy should know if this is still true, he uses an edited blizzard.j file to install the Commander to maps.