Portal: Replace last record with new data

[AlanP]

Background: We keep a running history (via a portal to another table) with all the work assignments an employee has and does work at. A big organizational change just happened an I only need to replace the departments of some employees CURRENT assignment (but not replace their old prior assignments in the same table which may have the same department I'm trying to replace).

Question: Is there an easy way to change their top level (first record) current assignment? Or because this is in a portal is it too difficult?