You can use a Union to 'sandwhich' two files with exactly the same columns together.
Thankfully this is pretty easy to do now in Tableau - Combine Your Data with Union in Tableau 9.3 | Tableau Software
Using your sample data as a guide though, you would actually need to prepare two separate tabs or files. Your 'main' data tab with say 30,000 lines then your duplicate 'Sub Accounts' data as a separate file/tab which is effectively an exact duplicate of the original 30,000 with those two columns changed.
If you manually prepare that second file, unioning them will be easy.
There is a way to achieve this through Tableau without the need for the second tab, but it's not ideal as it requires Custom SQL on top of Excel which itself requires the use of a 'legacy connector'.
Here's some reading material on what this means;
Once you connect to your file using the Legacy Connector, you can use the following custom SQL by using the 'new Custom SQL' option. It will dynamically achieve what you want with only one table -
SELECT [Group], [Sub-Group],[Name],[Identifier]
SELECT [Group], [Sub-Group],'Sub Accounts', 'Out Of'
Where [Data$] is the name of the sheet in Excel (minus the $ sign)
This worked perfectly. Yeah, unfortunately our server environment is still on 9.2. We haven't upgraded yet. I had to use a legacy connection to do the SQL Code.
Also, I had to edit yours to account for the metric gaps to fell them in with blanks (' '), in order to follow the same schema.