Once a major group is saved, you cannot change its type. The type designates all item groups and items that belong to the major group. Although you cannot change the type, you can delete and re-add the major group as long as it does not have any item groups assigned.
Over group assignment is based on the major group type selected.
The sales tax rate defined here is used in recipes that belong to this major group. This enables a more detailed cost calculation, including net and gross sales price.