Hi Raj,

The short answer is "it depends". Sounds like your question is based on some new government regulations that have come out and effect your company. Looks to me like its a standard case of "As-Is" and "To-Be" analysis. Then Gap (do a gap analysis) of the difference. Doing this will tell you if there has been a change to the processes or not (as you claim) and whether there is any change to the activities (functions) in the process.

I'd probably write a use case for any new functions you identify and just highlight any changes to existing functions. Hopefully you'll have existing use cases for the As-Is stuff so you can just change those use cases to reflect the changes but I expect you haven't. You then have to make a call at what point you write a use case for an existing function where the change is big enough to warrant the extra effort.

One other tip is to link the use cases, business rules and processes in your system directly to the regulations that effect them. Then next time the regulations change it is easy to see what processes and functions need reviewing.

Kimbo