The ability to dynamically adapt to resource variations is critical for modern-day mission-critical systems that operate in ever-changing resource environments. Test-based Software Modification (TBSM) is a recently proposed technique to build Resource Adaptive Software (RAS) that relies on existing test infrastructure, test labeling, and program modifications. TBSM is simple and applicable, but an inefficient technique; the primary reason for inefficiency is the sheer size of the search space. In this paper, we propose AdFL, a repurposing of Fault Localization (FL) that can shrink (and prioritize) the search space for TBSM more effectively than previously proposed heuristics. We present complete case studies and an empirical analysis of a set of open source projects as evidence that AdFL can significantly reduce the search space in TBSM. We show how to combine AdFL with previous heuristics for TBSM, and propose an incremental, best-effort variant of TBSM that uses AdFL to prioritize the search.