It seems that data in DAG accounts is static and doesn't change. How can I test account refresh without using real financial accounts, with DAG only?
You must upload your own transactions XML. It can be painful and tedious.
From the DAG site find a site of the appropriate container you are interested in testing and download the file. In your favorite XML editor you can add/edit transactions and then upload (via Edit).
A fair warning, the data that results from your upload may not necessarily prepare you for the real world transaction data. Also, if you stray from their undocumented format for the transactions there is no warning/error message and will simply result in empty transactions or whatever was previously uploaded.