1. A computer program product, the computer program product comprising a non-transitory computer readable storage medium having program code embodied therewith, the program code readable by the computer to perform a method comprising: fetching, by a processor, at an address specified by a program counter a prefix machine instruction and a first next sequential instruction (NSI), the prefix machine instruction and the first NSI defined for a computer architecture, the first NSI directly following the prefix machine instruction in program order; and executing the fetched prefix machine instruction and first NSI, the executing comprising a)-c): a) modifying a field of the fetched first NSI based on a value specified by the prefix machine instruction to produce a modified first NSI; b) executing the modified first NSI; and c) incrementing the program counter to point to a second NSI, the second NSI directly following the first NSI in program order; and executing the second NSI.