Most enterprise modelling tools hard-code their notations and meta models, making adaptation slow, expensive, and technically demanding. This paper presents an advanced meta-meta model — the foundational layer that governs how modelling languages and tools are defined — designed to support arbitrary meta models, multiple visual representations, multi-level modelling, and runtime adaptation without specialist programming skills. Targeting a property graph implementation, it draws on two decades of experience with the EVA toolset and a systematic review of leading platforms including Eclipse, MetaEdit+, and XModeler.