I propose the addition of "Nasheed" into the list of categories. This type of songs are considered Islamically permissible and they could be described as chants relating religion, religious culture and modern events which do not contain any musical instrument. It may be argued that there are not much of these, or that it is not popular, yet they have a distinct spectrum of listeners and are clearly distinguished from any other type of music. So I would be glad if it is added on.
With "category" you mean "genre"?
Feel free to add your "Nasheed" as needed:
Tools -> Options -> Genres -> Click on the "New" Button (the one with a golden star) and enter whatever you think is useful for your collection.
I do not think that quantity matters - but please see also the release notes on an earlier version:
There is a fixed set of genres for ID3V1 tags represented by one-byte-numbers.
There is no such restriction for ID3V2 tags so you are free to do as @LyricsLover described.
These user-defined genres for which there is no one-byte-number will be displayed as "Other" in ID3V1 tags.