I worked at an archive with a few million photographic originals in all kinds and forms and we did something that resembled this (besides storing it in our collections management system). Actually, the filename was prefixed with exactly what you’re proposing: letters representing the type of media, i.e. 24x30 cm glass plate negative.
I’ve come to the conclusion that this is impossible to accomplish natively in dK. Instead, try looking at software called AnalogExif, which will allow you to enter all of the Exif data you need to into a scanned file. Not just scanner info, but also your originating film camera, lens and associated exposure values. It works great for my purposes.
I have a similar situation with thousands of slides and negatives that I’m cataloguing with digiKam. The solution that works for me is just to use tags. In this example I’ve set up tags for the film type and size. You could also set up tags for the box or slide page, year etc. For instance, if you selected a a certain slide page in the left panel, digiKam will display all the scanned images on that slide page.
If this is all you want to document, you might want to look at EXIFtoolGUI. The EXIFtool documentation also lists the relevant tags, you might want to use for this pupose.
But I think it is more relevant to document also the “who, where, when and why” with the scans. I use geosetter to tag the geographic position (“where”) and I use EXIFtoolGUI with my tailored workspace tags to document the images for “who, when and why”, like this:
Just put the pages on a light table, add an overhead light and shoot. To get rid of the reflections, which are there in the top row of slides, use cross polarization, i.e. a sheet of polarizing film on the overhead light, and a circular polarizer on the lens.