This Blog post should give you an idea about how to set a user status based on a system status.
The Business requirement was to set a user status when standard button of 'Set to completed' was used on a business transaction ( screen 1). As per standard SAP on click of 'Set to completed' button system just updates the system status as 'completed' and leaves the user status as it is which was confusing the agent as the particular activity goes under 'Completed activities' assignment block (screen 2)..
The requirement was achieved via below config itself:
Config Transaction CRMBS02 has an option to configure Transaction Control the user status. This
allows the System Status to drive the User Status.
To do this select the User status ( configured for your transaction) you want to effect and either double click the user status or choose the Transaction Control option from the Goto menu option.
From the transaction control screen ,select create and you will get a list of System status’s choose the one (or multiple) that you want to effect and set the option buttons to Allowed and Set.
So, I set 'Complete' transaction control on User status 'CLBR'. so whenever a user selects the set to completed button from Web-UI, system will automatically set the user status to 'CLBR' i.e 'Completed'..
Similarly, as you can see there are lot of controls that can be achieved from this process.