After publication of your new timetable, you can simply copy all duties and time-offs, which have been already set in online substitution for previous timetable. Teacher details
You can do so in "Settings" - "Timetables" . There you can choose your targeted timetable (into which you wish to copy these duties), then Select "Tools" - "Copy: Duties and time-off" .
In new window you can choose source timetable.