In recent years, Industry 4.0 has gained relevance in the manufacturing sector. On one hand, it is expected that this new paradigm will affect the entire value chain and increase the capabilities of the manufacturing system as a whole, in terms of interoperability and communication throughout factories and beyond. On the other hand, considering that small and medium-sized enterprises represent one of the main forces in economic development and employment generation, focus is shifting toward said manufacturing paradigm in order to ensure competitiveness in the market in the nearby future. However, economic factors could stand in the way of this migration. Thus, digital retrofit is seen as a possibility for the integration of Industry 4.0, paving the way for unappealing technologies to large investment opportunities. In this article, a thorough literary review is performed regarding the formal implementation of Industry 4.0 applications. The result is the Asset Administration Shell model. Afterward, a methodology is proposed for the design and implementation of the Asset Administration Shell, leading to a digital retrofit approach for manufacturing resources. Finally, the methodology is applied in a turning station, thereby validating an increase in the communication and interoperability of the station, which can be used to add overall value to the manufacturing system.