1. An extendible microprocessor system comprising: a microprocessor including a microprocessor instruction set; and an extension interface coupled to the microprocessor, the extension interface including customized processor instructions adding functionality to the microprocessor instruction set included in the microprocessor, the customized processor instructions associated with an illegal instruction exception and an extension disabled exception, the illegal instruction exception indicating that access to one or more of the customized processor instructions is prohibited and the extension disabled exception indicating that one or more of the customized processor instructions is available; a system coupled to the microprocessor via the extension interface, the system configured to: generate, based on whether one of the customized processor instructions is required by a program, either the illegal instruction exception or the extension disabled extension when the one of the customized processor instructions is requested by the program; and perform, responsive to the extension disabled exception due to the program requiring the requested one of the customized processor instructions, context switching of data contained within the requested one of the customized processor instructions.