The production of spare parts using Additive Manufacturing (AM) is an emerging area that impacts the supply chain management. To give designers a way to proceed at the moment of redesign and produce a spare part using AM, this contribution presents a methodology for the design and manufacturing of digital spare parts using AM in decentralized facilities. The redesign of the spare parts is tackled by giving design considerations based on agile hardware development practices to improve the quality of the spare parts and reduce the lead time. Since this methodology is derived from different case studies of the military over two years, the approach is suited for the defence industry but can be adapted to other industries that operate reduced facilities abroad. Additionally, three different use cases following the methodology are presented. The weaknesses of the processes are highlighted and some recommendations for production engineers and designers are given.