Perhaps this needs to be spelled out in more detail. Edited:
CBV is an archive format. You can extract a .cbv file using ChessBase Reader (or paid ChessBase). Then ChessBase Reader can play through the resulting database, but to edit it as desired you would need a paid version of ChessBase (although it doesn't need to be the latest version).

If you don't have a paid ChessBase, another option is some free database program which can handle .pgn files. Instead of downloading the .cbv files from chesspublishing, you can download the individual .pgn files covering the same lines. That's not as handy as the "playable ebooks", but the information is substantially the same (assuming you grabbed all the relevant PGNs), and you are not tied to ChessBase.

How do you use CBV files? You can import the file into ChessBase. Perhaps you could edit the file to your satisfaction there. I would probably want to work from a copy while retaining the original.