The multiselect.add() method adds an event to the list of selected events.
DayPilot.Scheduler.multiselect.add(e, dontRedraw);
For bulk operations, use dontRedraw = true and call multiselect.redraw() after all changes have been made.
Select an event manually in an EventClick handler.
JavaScript
dp.onEventClicked = function(args) { dp.multiselect.add(args.e); };