The only software that can open and potentially export .mepj files is actually the very same software that made these projects, the Movavi Video Editor, in version 23 or newer. The software allows users to export their projects to several formats, including original MPEG format, so mepj to mpeg conversion, or export is certainly doable. As with other similar project file types, no other software can help you with this.
Updated: October 25, 2023