I think the easiest approach is to create the Requirement Type using the "Requirement Type" entity in customization, which allows you to assign an icon to the new requirement type. You can then use VB to modify the workflow based on the assigned "requirement type id".
Select "Requirement Types" > New > Properties-Assigned Icon: Replace. You can select an existing requirement types to change it's icon and rename too. Don't change the default "Folder" Type, as there appears to be system workflow associated with use of the "Folder". I've "broken" the requirement types by changing/deleting the default "Folder".