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Dynamic instruction stream editing (DISE) is a cooperative software-hardware scheme for efficiently adding customization functionality $e.g, safety/security checking, profiling, dynamic code decompression, and dynamic optimization - to an application. In DISE, application customization functions (ACFs) are formulated as rules for macro-expanding certain instructions into parameterized instruction sequences. The processor executes the rules on the fetched instructions, feeding the execution engine an instruction stream that contains ACF code. Dynamic instruction macro-expansion is widely used in many of today's processors to convert a complex ISA to an easier-to-execute, finer-grained internal form. DISE coopts this technology and adds a programming interface to it. DISE unifies the implementation of a large class of ACFs that would otherwise require either special-purpose hardware widgets or static binary rewriting. We show DISE implementations of two ACFs - memory fault isolation and dynamic code decompression - and their composition. Simulation shows that DISE ACFs have better performance than their software counterparts, and more flexibility (which sometimes translates into performance) than hardware implementations.