Economy Plus would allow you to make a free confirmed change to a different flight from midnight on the day of departure (known as FCOD).

Unfortunately this seems to be interpreted/applied as midnight UTC, which means you might need to get up in the middle of the night if you want to rebook onto early morning flight as Athens is UTC+3 in the summer... (UTC+2 during winter).

Other than that, assuming you have Oneworld Sapphire or Emerald status, the only other real benefit is that it includes 2 checked bags rather than 0 for Economy Basic.