I think it is an offence to disrupt these guards.
The Guard always takes precedence in all military parades. Their march style consists in normal march time, and at intervals, for several paces, striking the ground forcefully with their right foot. Their standard marching music is the "Evzonaki" ("little Evzone") march, played at 48 beats/min. They guard the Tomb of the Unknown Soldier round the clock. Guards on duty perform their movements in a very slow and highly stylized manner. They switch positions with each other every fifteen minutes and remain completely motionless and at attention in the meantime. Since the Guards are required to be totally still at all times, there is one Evzone in normal fatigues uniform and police surveillance to ensure that no one approaches or harasses the Guards while on duty. The "little changes" take place every hour on the hour, and involve the two incoming and two sentries, and a supervising "Corporal of the Change". The Grand Change takes place at 11 am on Sunday mornings, and involves the whole Guard with its officers and a military band, all marching from the Guard Barracks to the Tomb for the Change, and back. The Grand Change is a popular Sunday morning spectacle for Athenians and tourists alike.
During a demonstration in front of the Parliament in 2001, a Molotov cocktail was thrown at one of the guardhouses. In no time, the wooden construction was engulfed in flames. The Evzone standing next to it didn't even blink his eyes, let alone move, until the guard in standard uniform came and gave him the order to move. With a scorched and partly smoking uniform on one side, the Evzone did.
In January 2010, a makeshift bomb was placed 20 meters from where the Evzones guard the Tomb of the Unknown soldier, at Syntagma Square. Although the police informed the Evzones of the imminent threat, the Guards refused to leave their posts and remained on guard while the bomb exploded.
"Changing of the Guard - Hellenic Parliament, Athens" - Videos - Viddler