[BetterRed]

I don't understand why you want to carry it as a badly formed ISBN in the IDs - what are the advantages

ISBN numbers have an internationally agreed format, they are issued by the appropriate national authorities and if you click on them in Book Details they do a look up on the Online Computer Library Centre's World Catalog site.

If you want your version number represented as an a identifier then why not label it as myversion:. But I cant see the advantages of that over a simple custom column called myversion - and its much easier to display in the Book List, book jacket, catalogue etc, than using a template every time to extract it from the identifiers list.

IMO the only ways you might achieve your long term goals are a) to use the command line programs and some scripting, or create your own version of calibre from source.

BR