How to change a field value in a BC when a MVF is getting updated

We are using Siebel 8.1 and we have a requirement to change a field value in a BC field to a different value, when a Multi Value Field is getting updated. In the Docs it says that user property 'On Field Update Set' does not support MVG. Is there any other way to update, like scripting?

Requirement is like, when the Assignee MVF is updated with a value, we want to update the Status field to 'Assigned'