This seems to be a game that cares about its setting rather a lot, and there's no context where some worm as-yet unworthy of Valhalla gets a say in the creation of Valheim, a place that already exists in-context. Maybe after you've completed the game and cleansed Valheim of Odin's foes would you be given a say, but I doubt you want world gen options unlocked 200 hours after the world has already been generated.

TLDR: Don't hold your breath waiting for extraneous options...