Defining a language without structureLanguage

I'm trying to design a family of domain-specific languages.

It would be much easier to define these languages not in terms of ConceptDeclarations, but  in a different way, with more domain-specific editor,  because their structure is very similar. So it's a task for creation of language for definition of other languages.

Is it possible with MPS?

To be more specific, my languages are would be schemas for defining a hierarchy of data like

abstract concept Element extends NamedConcept

concept AtomicElement

  dataLength: integer

concept CompositeElement

  elements: aggregation 1..n of Element

(somewhat similar to xml...)

So, custom concept declaration editor should not contain "links", "properties", etc, but only UI for definition of such schemas.

Then, a goal is to create models conforming to such schemas.

I tried to extend ConceptDeclaration and create MyConceptDeclaration and editor for it, but I can't figure out how to extend ConceptDeclaration...