There is a Delete Override checkbox that can be added to the page layout on batches that allows a batch to be edited to a lower amount of Total Items after the batch has already been created and saved. To have this box set as checked for every batch creation, you will need to setup a workflow.

Go to:
  1. Setup, App Setup, Create, Workflows and Approvals, Workflow Rules
  2. Click New Rule
    • Choose Object: Batch, click Next
    • Rule Name: Delete Override
    • Description: Auto-check the Delete Override box to allow editing of Total Items in a batch.
    • Evaluation Criteria: Created
    • Rule Criteria: Batch: Total Items GREATER THAN 0
    • Save and Next
  3. Click Add Workflow Action dropdown, and choose New Field Update
    • Name: Delete Override (unique name will auto populate)
    • Field to Update: Delete Override
    • Checkbox Options: select True
    • Click Save
    • Click Done
  4. Click Activate
All batches created will now have the Delete Override function selected.