In version 2018.08 it was possible to build own actions with own logic (see https://docs.microfocus.com/itom/Service_Management_Automation_-_SM:2018.08/Add-custom-actions_19895075). In the newer versions e.g. 2019.08 this is not possible anymore.
But in my opinion it is important to create additional logic or connections to the Service Manager besides the OOTB Backend SM actions:
Close request: Close the request with Closure Code "Cancelled"
Close to Fulfilled: Close the request with Closure Code "Fulfilled"
Update to Dispatched: Change the request status to "Dispatched"
Update to In Progress: Change the request status to "In Progress"
Add activity log: Add comments to request
For example we would like to add a new button to cancel (not close) an interaction. The OOTB Close Request Backend process calls up a process that is "wrong" for us, because closing it still opens the related record (in our example an Incident).