No, you may not delete any employees from a correction batch. If you need to list an employee under a different company, simply add them to the correct company and do not correct them in the old company.
You also may not add any employees to a corrective batch. If you need to add an employee, please set up a new "dummy" company, add the employee and create a new batch.
Note: If you wish to use the .csv uploader to add many employees, within your "dummy" company, please use a fake EIN at first; so that the employees will be uploaded to that EIN, then simply change the EIN to the correct one on the 1094 form manually before locking the new batch.
