University-based FabLabs are frequently described as open access spaces aligned with the Fab Charter, yet within universities, openness is shaped by safety regulations, liability frameworks, and institutional governance. This paper examines how openness is operationalized over time through a ten-year longitudinal study (2015–2025) of a university FabLab in Japan that transitioned from a suburban campus facility to an urban-facing fabrication space within a publicly accessible co-creation environment. Drawing on boundary work theory, institutional work, and commons governance, the study proposes a three-layer boundary reconfiguration model encompassing spatial embedding, institutional codification, and participatory mediation. Participation records show external users growing from 11–23% to approximately 28% after relocation and governance redesign, alongside total users increasing from roughly 1,100 to over 3,300. The findings demonstrate that spatial visibility alone does not produce openness; durable openness emerges only when spatial, institutional, and participatory dimensions align. The paper reframes openness as a governance achievement rather than a normative attribute, offering a processual model for how university FabLabs can function as civic infrastructures within regulated environments.