Thank you for your forum post.
The primary ideal behind SQL Data Generator is for the user to be able to generate realistic test data to populate selected tables or entire database. It is not a tool for merging data together.
However, you can add extra rows to the existing data. In the Table generation settings, uncheck the "Delete data from table before generation" check box and select the required data you wish to add using the "Use existing data source" option as the source of data.
Migration scripts are used with SQL Compare and SQL Source Control to prevent data loss when making a change to a specified table or merging / splitting tables or changing the data type of a column.
The migration feature has a new beta version called 'Migrations V2', if you wish to try ou the beta, please visit this web PAGE.