Adding a Role to a Category-Commodity-Person relationship

In Oracle EBS, 12.2.5, I can create a Commodity, and then assign one or more Categories to the Commodity, and then assign a Person to the Commody, but the only Role I am able to assign a person to in the relationship is "Commodity Manager", which apparently is a default role. How can I create additional Roles that I can then assign to a person, to differentiate how different people are expected to interact with a Commodity?