I too would have preferred the option to edit existing characters if for no other reason to retain their existing claims. Some characters are set up to inherit a title. When you change that, you're making a substantial change to the balance of the area (if there ever was any). It would be great to be able to add claims in the Ruler Designer, but I'm sure that would be difficult to implement and would be easily abused. Allowing the editing of existing characters, while retaining their non-editable statistics (like claims) would be the best way to go.