Retire artifact types

One way that occurred to me is using the project administration, and under the permission option on the left hand, select the role(s) you want to block (author probably), and under the "Requirements Management Resources" heading -> save artifacts -> create an artifact -> create an artifact of a specific type, and revoke the permission for the types you want to retire. You can leave "delete" and "modify" as is, so existing artifact of those types can be worked on.