If your Tivo is completely unmodified then I believe there is a way to get a Bash prompt over the serial connection but I'm not sure if you will be able to ftp back and forward as I believe that ftp is part of the network drivers installation?
If you can get a file on there then running Blindlemon's set up mode 0 script (see the Mode 9 thread here) will do it all for you.
Editing anything without installing something like Joe to edit files on the Tivo isn't going to be possible (I dont think) as there are no built in file editors in a standard Tivo and there are no 'public' interfaces for a windows program to interact with if you've not installed TivoWeb.
I guess the short answer is "no" I don't think you can do it .
You might find some better info here...