I've been trying to find if there is some system in game to change physical appearance (e.g. hair, face...) of your character once it has been created. Maybe through some special item or NPC.
Is it possible?
Nope, not yet.
I'm certain that this will be added at a later date, but it's pure speculation. At time of writing the choices you make during character creation regarding visual appearance are permanent.
Yes, yes you can.
Recently released are the 'Self-style hair kit' and 'Total makover kit' purchasable from the gem store.