I don't think you'll find an answer to this specific question in the forum, as I don't remember anyone who ever wanted to add film type information.

The question is: what format do you want the information stored in, and what needs to be able to read this? I would suggest creating a custom tag of your own to store this information, but if you do this the only format which would possibly allow other software to read this custom information is XMP. So if this was me, I would create a custom XMP tag called FilmType and use that.

If this sounds like what you want to do, look at the config file documentation for an example of how to create user-defined XMP (an other types of) tags.

- Phil