Typical processes controlled by hard real-time computer systems undergo several, mutually exclusive modes of operation. By deterministically switching among a number of static schedules, a pre run-time scheduled system is able to adapt to changing environmental situations. This paper presents concepts for specification of mode changes, construction of static schedules for modes and transitions, and timely run-time execution of mode changes. We propose concepts for mode changes in the context pre run-time scheduled hard real-time systems. While MARS is used to illustrate the concepts' application, they are applicable to a variety of systems. Our methods adhere closely to the ones established for single modes. By decomposing the system into a set of disjoint modes, the design process and its comprehension are facilitated, testing efforts are reduced significantly, and solutions are enabled which do not exist if all system activities of all modes are combined into a single schedule.