What url should I use to retrieve the values of Impact?

I'm working on a client using Change Management REST APIs (https://jazz.net/wiki/bin/view/Main/ResourceOrientedWorkItemAPIv2) to communicate with RTC.

My environment setup is as follow.
The processes defined for the projects are Scrum and OpenUp Process correspondingly and the values of Impact field for Scrum/Adoption Item are Minor/Moderate/Significant/Major vs Low/Medium/High for OpenUp Process/Risk.

Looks to me that the url to access the values of Impact field is different in Adoption Item from Risk type of work item.

Url for the values of Impact field for Adoption Item:
https://localhost:9443/jazz/oslc/enumerations/_kDbZkI-fEd-F89pXTeqXtA/impact.xml

Url for the values of Impact field for Risk:
https://localhost:9443/jazz/oslc/enumerations/_GM7lIAyJEeCqiMP4KrF8-A/risk.xml

Here is my questions.
1. Is this url or values configurable through project setting or else? And how, if yes?
2. Is there any way using REST API to determine which url I should use instead of hard-coded?


Thanks a lot.