CREW TIMELINE panel has now a new functionality: REPLACE CREW - it can be used for smooth & quick replacing assigned crew with the other crew members.
To replace crew, mark a flight (or flights) and right-click with the mouse, then select 'REPLACE CREW' option.
Leon will show a pop-up screen with names & codes of assigned crew - click on a field next to it (showing 'No change') and a drop-down list of available crew will show. Leon shows only crew with ratings for the aircraft assigned to the selected flight.
Select crew and click 'SAVE' - a confirmation of replacing crew will show in top-right corner of the page.