To change reporting times (Report On/Report Off) for all assigned crew from default values to the manual value, go to the right-hand filter, tab CREW and click a link SELECT ALL. Here open a section FTL CALCULATIONS and click a button and add new reporting times, which will apply for all crew assigned to the trip.
Once new reporting times have applied, if you add a new crew member to the trip, he will have those new reporting times assigned.
Using an option of manual split/merge defining by clicking the icon is not possible in a 'SELECT ALL' panel - it is possible ONLY when editing a single crew reporting times.