We are presenting a new concept of an application-specific processor that is capable of transmuting its instruction set according to non-predictive application behavior during run-time. In those scenarios, current (extensible) embedded processors are less efficient since they are not run-time adaptive. We have identified the instruction set selection to be a critical step to perform at run time and hence we focus this paper on that crucial part. Our paradigm conducts as many steps as possible at compile/design time and as little as necessary at run time with the constraint to provide a sufficient flexibility to react to non-predictive application behavior efficiently. We provide an in-depth analysis of our scheme and achieve a speed-up of up to 7.19x (average: 3.63x) compared to state-of-the-art adaptive approaches (like [19]). As an application, we have employed a whole H.264 video encoder though our scheme is by principle applicable to many other embedded applications. Our results a...