Hi,
I can tell you the scenario when we need to chane the JSESSIONID cooie name.
We have a weired application set up like a main application in which other application having different context opens as a TAB.
So 2 different applications runing within a same browser session.
We put IIS as proxy to route the request for both the applications.
IIS is pretty messy and changes the JSESSION when you switch between 2 applications. To overcome this problem we chane the cookie name in weblogic.xml for one application and it solved our issue.