This thread talks about a similar problem: Is it possible to include dynamic list of Excel files as data sources? If now, what would you do to include data from it… . There are 2 differences:
1. Instead of using addfiletoextract, you can use refreshextract from the Tableau Command Line Utility and send the new filename as part of the instruction.
2. Because the name of the file can change, you can use the command line to list the files within a folder a perform an instruction for each. This is outside of Tableau's realm, but this thread shows an example: command line - How to loop through files matching wildcard in batch file - Stack Overflow
Hope this helps!