Firstly, the metadata that Kobo reads from sideloaded books is fairly limited. It is mainly the core metadata. It doesn't include things like series info or any custom columns that calibre can add. But there are ways to do it. How depends on what you want.
The things I can think of are:
- Creating a collection for each interest level as @Colonel Cathcart suggested.
- Using the subtitle field as suggested by @John F.
- Adding the information into another metadata field such as the comments.
The first two are done through the driver configuration. The last one can be done using a metadata plugboard. There are advantages and disadvantages to each method. Which you use depends on which works best for you.