This is to rename blocks already in the current drawing, not to rename DWG files in a folder.
My understanding from the OP was that he'd like to see a preview of the block he wants to rename (unlike only showing its name in the normal rename dialog).
Are you looking for something to allow renaming DWG files in your block library? Or rename the blocks contained inside DWG files in your library? The 1st would be reasonably simple, the 2nd would require some ObjectDBX.