We have a button Decline in one of the screens and on the actions, we have a local action and finish assignment when Decline Submitted, property which will set when the user clicks on submit in the local action. Is there a way to configure this in such a way that the finish assignment works conditionally.
The Finish Assignment condition on the Decline button does not work because that condition is checked before the local action is completed and before the property is updated. Use the Decline button only to open the local action. Then, on the Submit button inside the local action, set the Decline Submitted property and call Finish Assignment there. This makes the assignment finish only after the user submits the local action. In simple terms, move the Finish Assignment step from the outer button to the local action’s submit flow. That is the correct way to make it work conditionally.
In Constellation, you can’t add buttons like this, nor for finishing assignments (you can only change label for OOTB buttons).
I know you are in Traditional UI here, but you might want to consider a design that prepares for the future. Although feasible, it does delay the redesign effort to when it will be more costly and you may have more resistance (as users are used to this button).