We can reassign screen flow using Reassign OOTB activity to worklist (or using pyReassignAssignment to WB/WL). But previous assignments and next assignments would be routed to previous assignee. In order to route to modified assignee change the DefaultAssignTo property value from old operator to new operator. You can find it in pxFlow - pyFlowParameters - DefaultAssignTo.
To identify flow whether it is standard flow or screenflow use pyCategory.