The Ricercar Lab - the musicological research team at the Center for advanced Studies in the Renaissance at the University of Tours - has decided to make available in open access, thanks to the support of the French digital infrastructure Biblissima, a large corpus of about 3500 XML files of 15th-c. music. This corpus was produced by the German musicologist Clemens Goldberg who encoded since 2010 onwards the musical content of 34 major 15th-c. music manuscripts and other complementary files, in order to offer on his foundation's website PDF files of complete collections of works by Du Fay, Binchois, Okeghem, Busnoys and most of their major contemporaries, focusing on their secular output. This corpus was encoded in an XML format named CMME (Computerized Mensural Music Editing), specifically conceived for mensural music by Theodor Dumitrescu in the 2000s, together with editorial and publication tools which have not been updated since then. This article focuses on the development of a set of conversion tools for these CMME files to meet more up-to-date standards of music encoding, namely MEI. A workshop was organised in September 2024 at the Campus Condorcet in Paris, gathering experts with a wide range of knowledge on mensural music notation, XML formats and programming. A converter was developped directly in the open-source rendering library Verovio, allowing the conversion from CMME to MEI mensural. A conversion to MEI CMN was implemented afterwards, enabling to load these files in common engraving softwares such as MuseScore with minimal loss of information. With the availability of a direct import of CMME-XML into Verovio, the corpus of existing CMME files gets a new life. Furthermore, since the stand-alone CMME editor still works fine and no alternative is available yet for native MEI, the converter offers a new pipeline for encoding and editing mensural music.