I could see FilterHistory decision tree referencing "AssignmentRouted", it will be called if the production level is 2 and the System Setting FilterHistory value for level 2 is "WRITE_SOME", which is the default. I was looking at a Pega 8.1.x environment, not sure what version of Pega you are running.
Thanks Kevin. But I am more interested in the invoking of this field value so that I can pass my intended param values. Decision tree reference is more on whether it can be invoked or not but not the actual triggering point.
If you are looking to find a way to customize AssignmentRouted, currently there is no way as it is referred via Task_Assignmment --> AddHistory functions which are final. Probably you can call extension activity pyAddWorkHistoryDefaults before commiting history record which is commited in AddHistory. But AddHistory is common function invoked for history, care should be taken while overriding this activity as the same will be called from AddWOrkHistory.