Embedded systems including IoT devices are designed for specialized functions; thus, changes in functions are not considered following their release. For this reason, changing functions to satisfy the requirements of IoT systems is difficult. In this study, we focus on updating existing embedded systems without modifying them. We investigate the design of new functions and their implementation with limited resources. This paper describes an evolution mechanism for updating the functionalities of existing embedded systems. The evolution mechanism uses a control unit that is deployed outside the embedded system. To guide the steady implementation of the evolution mechanism, we define an evolution process that effectively uses the state machine diagram at the design time and runtime to update the embedded systems. The programming framework implemented in this study supports the evolution process. We evaluate the evolution mechanism based on the results from two experiments. The first experiment involved applying the evolution mechanism to a cleaning robot, this demonstrated that the evolution mechanism systematically enables the injection of new functions into an embedded system in the real world. The second experiment, on the probabilistic model checking, demonstrated that the mechanism provides almost the same performance as the ordinary embedded system with an improved robustness.