is it possible to target a player as if they were a Planeswalker?
No, you cannot target a player as if they were a planeswalker, and you cannot target a planeswalker as though it was a player. Saying that players are "planeswalkers" is simply part of the flavor of the game.

That being said, there are a couple of ways in which the rules treat planeswalkers as similar to players. While declaring attacks, you may declare that a creature is attacking a planeswalker instead of a player. That creature can be blocked by creatures the planeswalker's controller controls, and it deals combat damage to the planeswalker instead of the player. This is specified in rule 508.1b:


  If the defending player controls any planeswalkers, or the game allows the active player to attack multiple other players, the active player announces which player or planeswalker each of the chosen creatures is attacking.


In addition, if a source you control would deal damage to an opponent, you may choose to have that damage be dealt to a planeswalker that player controls instead. This is specified in rule 306.7 (from the reversed perspective):


  If noncombat damage would be dealt to a player by a source controlled by an opponent, that opponent may have that source deal that damage to a planeswalker the first player controls instead. This is a redirection effect (see rule 614.9) and is subject to the normal rules for ordering replacement effects (see rule 616). The opponent chooses whether to redirect the damage as the redirection effect is applied.