How to move customized work item from one project area to another
One answer
If it is the work item type you talk about then you can do a diff of process configuration sources of both the project area (outsuide RTC by copying them and diff via your fav comparison tool)
Then you can then add the differences to the new PA using Eclipse client on the "Process Configuration Source" tab.
I wouldn't recommend this as if you make simple mistakes, then the PA will go for a toss. Of course you can recover by going back to prev state but lot of work.
Alternatively you can think about "Process sharing" between multiple PA's