It is possible for you to change the case owners for Learners in bulk. To do this you can use the Upload Users functionality in the Users Overview tile. You will only need to include the following columns in the upload form:
Please note that the User ID is not included in the default upload form, so this will need to be added in manually, as the first column.
Once this information has been filled in, you can then upload the form and the case owner for the Learners will be updated, without causing any duplicate records.