In a one-year field study of four long-term care facilities, we examine the process by which managers in small- and medium-sized establishments (SMEs) can change their existing HR systems to develop human capital. Research on strategic HRM and human capital has identified high-impact practices that promote employee commitment and involvement, and it has focused on how managers draw on existing capabilities to achieve vertical and horizontal fit in HR systems. In contrast, we perform a grounded analysis of the change process and identify variation across establishments during the implementation of a new online training program. While all four of the facilities in our study adopted ability-enhancing practices (selective recruitment, extensive training) during the pilot phase, only two facilities successfully integrated their pilot programs into regular operations and adopted additional high-impact practices that promoted employee commitment and involvement (expanded promotion pathways, mentoring by incumbents). We explain this variation by identifying that incumbent HR and training members may be vested in their traditional practices, which makes the development of new capabilities difficult. We find that HR managers in SMEs can address these incumbent firm adaptation challenges and successfully adopt high-impact HR practices by engaging in what we call greenfielding – first separating new investments from daily operations, and then later reintegrating them. Counterintuitively, we suggest that this may be more challenging for establishments within larger and formally structured parent organizations.