I have been trying (unsuccessfully)  to update a pricebookentry id (product from one pricebook) on line items using the data loader.  I tried update, but that field is not updateable. I also tried upsert, but i receive an error > Unable to create/update fields: PricebookEntryId. Please check the security settings of this field and verify that it is read/write for your profile.

Am I doing something wrong or is there another, better way to do this.....

Thanks in Advance!! I hope this makes sense

~mike