RE: Is there a way to add fields to entries that are not a Custom Field?
Not sure I understand the question… if you add a field to the entry which is not a “core” field or a field within a “core” fieldset, it is a custom field.
RE: Is there any way to import a CSV file and import Data into a Custom Field that Has been setup?
Sure, here’s a link to a developer doc which covers adding custom text field, how to display it and how to register with with the CSV import/export features.
Hope this helps!