Hi,
Unfortunately, this is not available out of the box for Change Management.
To achieve this you would need to request an open version of the Change Management project from Symantec, then possibly require assistance from a Symantec Partner that has workflow experience to make the required changes.
If the request isn't urgent, you could raise an idea for this and Symantec may take this into consideration for the next release of Symantec ServiceDesk. The link for the Ideas section is below. There is a button to the top left for Post New to create one.
https://www.symantec.com/connect/product/servicedesk?filters=type:idea
Thanks