Here we are not sure, if we understand the word “Meta-editor” correctly.

ADOxx provides a graphical definition language called “LEO” that enables the definition of graphical notation of modeling classes. Those modeling classes are then used in a concrete modeling toolkit to design a model and hence the graphical notation of that class is shown in the designed model. Samples are graphical notations of UML-classes, UML-interfaces, BPMN-activities, BPMN-event, or ERM-entity.

The graphical notation is defined in the so-called GRAPHREP attribute.
This is a class-attribute of the meta model. Initial syntax of the GRAPHREP is explained in the method tutorial, see slide: www.adoxx.org/live/documents/10157/d228d6f1-309d-45a4-a9b8-aa914a0634af, in /slides/ file “Modelling Language Implemenation, on slides 48pp.

In order to get familiar with this type of graphical notation language, there are some samples at:
http://www.adoxx.org/live/adoxx-graphrep-repository-wiki/-/wiki/GRAPHREP+Repository/FrontPage

The development of such graphical notation can be performed either:
(a) by implementing the code in the development environment of ADOxx (which is introduced in the tutorial slides),
(b) by drawing picture in other tools like powerpoint and transform those picture saved in emf format into leo using a Web-Service on adoxx.org platform:
(http://www.adoxx.org/live/adoxx-development-tools), or
(c) using the development tool at the OMiLAB (http://omi-repo2.dke.univie.ac.at:8080/svg2graphrep/) in the category services.

So the answer is, yes – ADOxx provides an environment to manually define graphical notation of the meta model.