Renaming .twb's is trivially easy. From Windows you can just right-click on the file name and invoke "Rename."
Or from within Tableau Desktop, you can Save As ...
Now, renaming the TDE's on the one hand is easy, but on the other hand will break any Worksheets that use the old TDE name as a Data Source. For those, you may have to Edit Data Connection to point the Worksheet to the new TDE. One way to ease the pain is to just Copy the TDE file to the new name, and then deprecate use of the old name over time.