Hi Faisal,
To separate out a request type for change validity, we had done the following for a customer:
1. Create a request type "Change Validity".
2. For this request type have actions as change user, user defaults only. This would eliminate the "Add role" option from the request form. It will only give the "Add System" option.
3. For the request type ID created have a different path in your BRF plus initiator.
4. New account and Change account remains same, for add roles and add system.
Let me know if this fits your purpose too.
Thanks
Sammukh