This study examines how buildings and streets in Yeji-dong, Jongno-gu, Seoul, adapted as the district shifted from residential to commercial use. The scope covers 184 buildings, 262 land parcels, and pedestrian-oriented streets/ alleys. Methods combine literature review with measured drawings, photographs, videos from prior documentation projects, materials collected during dismantling, and field surveys. Findings are as follows: (1) from the mid-1950s to the 1970s, vertical expansion (mixed-use shop-houses, party-wall buildings, and partial upward extensions) prevailed; and (2) in the 1980s–1990s, horizontal expansion intensified through additions/ alterations and building integration across parcels. Sectoral requirements (electronics, cameras, watches, and jewelry) directly shaped shop size and plan. The southwest electronics cluster favored deep plans with storage, and the northeast watches/ jewelry cluster featured small serial shops and intensive use of adaptive passages. Adaptive passages, non-statutory connectors formed outdoors or within buildings, are classified as dead-end, one-way, and multi-way types. They improved customer access and micro-logistics, structuring high-density commercial space. Zoning designation, road improvements, and redevelopment schemes mediated the spread of commercial functions. The study systematizes the concept of adaptive passage and elucidates self-organizing adaptation mechanisms of architecture and urban fabric under commercialization. Limitations include post-demolition constraints and reliance on prior records, and comparative studies in other districts are suggested.