After you initially setup, you can modify them however you wish inside the CDSEO Admin section, but never delete and repopulate. Only populate empty fields. This is useful for when new items are added.
If a field can't be filled in automatically, there must not be information available for it and it will need to be entered manually.
If you haven't already, I'd recommend installing this addon so you can modify CDSEO values in the X-Cart admin instead of the default values that CDSEO replace:
http://www.x-cart-seo.com/cdseo-pro-for-x-cart/xcart-admin-addon.php