We enable railway operators and manufacturers to modernize proven legacy systems for the digital future. For Siemens, we implemented an SCI-Converter (Standard Communication Interface) that extends existing axle counter software with EULYNX over RaSTA connectivity, without replacing the established core system. Through comprehensive legacy analysis and robust software architecture, we designed a scalable migration path for safety-critical systems. Our approach combines comprehensive software-development with parallel development of Unit and Software-integration tests, executed alongside automated validation using a tailored RT-Tester environment. The result is seamless integration of modern EULYNX standards into proven legacy track vacancy detection solutions, enabling long-term digital transformation in rail signalling.