The newusers command is useful for adding or modifying users in bulk. Is there an equivalent command for managing groups?
I haven't run across one or a reason to have one. Then main use case for new users I have seen is to add the students for a class or some other group. They would normally all belong to the same group.
Groups usually have a specific purpose. Unlike users groups don't usually come in groups.
Do you have a use case in mind?