Model-Based System Engineering (MBSE) and particularly Model-Based Product Line Engineering (MBPLE) now stands as the new standard for systems engineering at Airbus Group. Indeed, the Airbus MBSE Architecture Framework (R-MOFLT) and its feature-based product line engineering framework extension (MBPLE4MOFLT) are widely deployed on Research & Technology projects. This paper tackles the applicability of such enablers to large legacy systems. As such, it outlines a proof of concept on redesigning a legacy system using MBPLE4MOFLT as a new product line based on several in-service variants definitions that have been designed over the last four decades following document-based ways of working. As such, the interoperability between these ways of working and the new digital assets is essential to achieve this migration on one side and, once migrated, to ensure backwards compatibility with the official process, on the other side. To this aim, besides using existing data hubs between Cameo Systems Modeler and Rational DOORS, the Airbus MBSE SysML profile has been extended with further customizations to fit the new product line design golden rules. Wizards are also proposed to ease authoring and impact analysis. Finally, a new plugin has been developed to automate the variability propagation throughout variable assets and to ensure consistency between the variability handled with MBPLE4MOFLT and the requirements applicabilities handled in Rational DOORS.