In the new SAP Release we have got some flexibility to change Priority of workitem dynamically. First we need to create a container element as shown
Then go to the relevant dialog step where you need to change the priority.
Then add the container element we just created and the one we will update the priority
Create a loop step such that the decision task will loop until priority is 1.
Reduce the priority inside the loop when the loop condition fails
Initialise the Priority with 5 which is default workflow priority before the activity step and before the loop step
Here is the design
The priority is 5.
After execution of the dialog step next priority is 4
Here is the workflow Log