Customize the drop down list for requirement types

Hello

I have another (probably stupid) question on the requirement type topic.

Once created the new requirement types, is it possible to restrict the choice of req type in the drop down list to only the newly created types? Since the list "feeding" the drop down list doesn't appear in the project lists I can't replace it with a customized list that would only consist of my newly created types.

What are my options to allow the customer to choose between my customized types ONLY ?

Thanks in advance for your help.