Hello.
I'm just wondering... How am I supposed to make it easy for a player to actually alter the game in a FPRPG where he customizably makes his own character from scratch.

I mean, in the future it cant really be like. "And so, the unknown hero slaught the fierce dragon and brought justice to the corrupt dictator of Ashgarl" This was a sentance I thought up as I wrote by the way.

Any ideas how to counter this?

I have been thinking about having a known hero follow the player during big events, but I dont know if that would be solid enough...

So your problem is about how to refer to the player?

Classic solutions to this is either giving the player a fixed last name or codename (Such as in Mass Effect or Deus Ex), a title ("Vault Dweller" in Fallout, or the goddamned "Hero of Kvatch (This is truly an honor)" from Oblivion), or have the game be text-based and just refer to the player as whatever name the player put in (Zelda).

Or refer to the reader of the design as "you."

Using synthesized speech is another way, but that is a hella long way off from actually sounding passable in a gaming sense.

Wanderer, Adventurer, Savior, Loner, Vault Dweller, You, Hero, Boy, Girl, Man, Woman, He, She... just to name a few off my head.