medium subtype

I believe most libraries manage this using Subject headings. Each Braille title is given a subject heading for the braille code used, and patrons are given an exclusion for any braille code they can't read (or just don't want to receive; I'm sure it'd be confusing to try to switch back and forth).

However, it should certainly be possible to treat them separate mediums as well. I recommend contacting Customer Support so they can walk you through everything that would be needing to switch one or the other type of Braille books to a separate medium (such as adding the new medium code, updating the titles, and updating the appropriate patron records).