@thomastc You can do it inside vim: https://vim.fandom.com/wiki/Bulk_rename_files_with_Vim
But the emacs way is better: open the directory in dired, press c-c c-c, you're now in edit mode, that is, the buffer with the directory listing is now fully editable, apply any modifications, press c-c c-c again to save the buffer, thus renaming the files.
Take a look: https://m.youtube.com/watch?v=Fm1K1crWKn8