The reason that the ancient skeleton recently discovered in Greece is so important is that it is a human skeleton found in a sacrificial altar. Archaeologists have been excavating a mass sacrificial pyre to Zeus in Greece, and if it can be proven that this human skeleton was a sacrifice it would be the first documented human sacrifice in Ancient Greece. It might significantly alter opinions on the history of Ancient Greece, which is not viewed as violently as that of Ancient Rome.
The past can be significantly changed by a skeleton. We can understand better what people looked like, what they ate, the activities they did and also when they lived. Any or all of these will change history - either by confirming what we know, turning speculation into fact, or challenging our views.
If archaeologists can find enough supporting evidence to show that the bones are of a sacrifice to Zeus, that might change how scholars and Greeks see their history. There are stories of human sacrifice, but it doesn't seem to have been a huge part of ancient Greek culture. Also, there is a possibility the bones were moved, or are from a different time than the surroundings in which they were discovered. It would be more significant if more such remains are discovered.
The skeleton will likely give us more insight into the past, but it is not likely to make any significant changes to how we understand ancient greeks. Scientists will certiantly study this skelleton for clues, but we already know a great deal about ancient Greece, and it is unlikely that much of this knowledge will change.