Can I redefine the data import process for an already imported batch and reimport it?

Yes. If the data is still available in the interface tables and the batch status is Preimport Completed, Completed with Errors, Error, or Terminated when Error Limit Reached, you can redefine the data import process and reimport the batch.

Once a batch has been successfully imported, you can't reimport the batch, even if the data is present in the interface tables.