You use the Data File Editor in the same manner whether you start with a newly created data file or an existing data file.
If you have a record layout file loaded, you can create a new record based on one of the record layout types, or you can specify padding bytes to fill the records. If you have created conditional record layouts and you choose your new record to be one of these, the condition field is set appropriately. For more information about record layouts, see Record Layout Editor.