|KOrganizer is the calendar and scheduling component of Kontact, the integrated personal information manager of KDE.|
KOrganizer provides management of events and tasks, alarm notification, web export, network transparent handling of data, group scheduling, import and export of calendar files and more. It is able to work together with a wide variety of groupware servers, for example Kolab, Open-Xchange, Citadel or OpenGroupware.org.
KOrganizer is fully customizable to your needs and is an integral part of the KDE PIM suite, which aims to be a complete solution for organizing your personal data. KOrganizer supports the two dominant standards for storing and exchanging calendar data, vCalendar and iCalendar.
While many things about an appointment can be changed, the time is the one thing that can't change for the remainder of a series of appointments (single exceptions are possible). KOrganizer uses the time field as a basic reference, so it would be difficult if not impossible to allow this change to happen.
Instead, then, create an entry for the start of the changed appointment, duplicating the information from the first entry apart from the new time.
A fuller explanation of the problem can be found here