Off the top of my head, that sounds like the sub-categories of the battle-use items would be read via a note-tag. For example, HP/MP restore could be one sub-category, and use a note-tag of "<category: restore>", while damage-dealing items could have a note-tag of "<category: damage>", or whatever.
Not 100% sure how that all would be implemented without doing some research on `Window_ItemCategory`, and probably `Scene_Item`.