It is possible, but it requires external tools to do. There are [various inven][1][tory editors][2] that let you change your player's name and appearance. And, of course, there are tools like [TEdit][3] that let you edit a world including the name.

Changing the profile/world filename will not rename the world and those files are encrypted so normal text editor will not do.


  [1]: http://www.terrariaonline.com/threads/1-2-tsge-terraria-save-game-editor.107906/
  [2]: http://www.terrariaonline.com/threads/released-1-2-terraria-inventory-editor.64501/
  [3]: http://www.terrariaonline.com/threads/tedit-terraria-map-editor.35394/