System fields values such as Category, Priority are managed under system tables named after each work item you are using. So if for example you wish to add a new value to the category of work item Requirement, all you need is to follow this post about managing system table values:
http://www.orcanos.com/help/Knowledgebase/managing-system-table-values/
Answer for How do add new value to item category
Author: Rami.Azulay
Expert in deployment of lifecycle management system into Medical Device vendors who seeking warranting successful Medical Device Auditing and Regulatory Compliance through Process Automation Tools It is no secret that Medical Device companies incur much costs and organizational stress relating to creating and maintaining their Technical File, DHF or ISO documentation, especially before first time submission or external auditing by notified bodies. https://il.linkedin.com/in/ramiazulay