As a none expert on Greyhawk can some explain to me please the changes and what they mean for the setting in regards to Blackmoore?
To be honest, we don't really know before we see the text. What is crystal clear from the map is that all metaplot geopolitical events after the original Folio/box set have been undone, which would match the setup on Ghosts of Saltmarsh, so it is a back to the original timeline reboot (countries that got wiped out in 1989 are restored, all countries are back to their original borders even if renamed).
Other than that, some of the changes are country names goijg from exonyjs to endonyms (the Tiger Nomads do not call themselves thsr, and their own name from the original Folio is the one on the map now instead of what the people fo Greyhawk call them, etc.). The Scsrlet Brotherhood has been renamed to the countrybname of Shar, which makes sense as that is like having called Thay "The Red Wizards" in a map.
Blackmoor, specifically, is the interesting exception was renamed Arn on the map, a clear reference to Dave Arneson. Unclear exactly hat that means until we have the text.
Broadly, the images and snippets have also demonstrated that Dragonborn and such are in Greyhawk retroactively, which is no shock.