Can I reset Dragon Age Keep, or it's default Characters?

IF you are just looking for a default state for the next game, then simply don't import a character and it will use default....if you mean something else, then sorry, and maybe a bit more info on what you want.

Descriptions for your characters in the Keep isn't all that important other than to keep them separated, as It to my knowledge doesn't get imported into any games.  So other than maybe changing names and modding your tapestry, you really don't need to have all that much info with them....