Because there is a need for engineering changes to fix design errors and satisfy design constraints even after chip fabrication, design flexibility and debuggability are extremely important to provide reliable designs and shorten time-to-market. In this paper, we propose a new VLSI architecture called field modifiable architecture (FMA) and its design method. Because of the nature of reprogrammability in FMAs, all of the engineering changes in designs are resolved at specification-level in terms of code recompilation. As a result, engineering changes even after chip fabrication are realized easily without wasting design time. In the experiment, two examples of engineering changes are demonstrated to investigate the efficiency of our proposed method.