In France, the railway lines are divided into the national and international lines. While the former has a proper implementation of the railway signalling systems as relay-based or computer-based systems, the latter follows the guidelines defined by the ERTMS standards, focusing on the interoperability throughout Europe. In a previous work we presented how the national legacy relay-based Railway Interlocking Systems (RIS) can evolve to use a computer-based technology in order to benefit from its advantages. In this present article, we present how these computer-based systems can be used in order to allow the evolution from a national line towards an ERTMS compliant international line. This proposition is based on the fact that the previous work provides the support for evolving the track-side technologies with, for instance, the use of GNSS for the train geo-localisation instead of electrical circuits-based train detection systems. Then, a discussion of the impact of this evolution over the system safety is presented.