The metamodel editor lets you edit the metamodel that is in use for your active workspace.
Opening the Metamodel Editor
There are two ways to access the metamodel editor.
From the navigator
You can right-click on the workspace name in the navigator, then select “Edit metamodel”:
From the main menu
Select “Manage component types and metamodel” from the dropdown menu:
Editing the Metamodel
You can (1) add another top level component type by clicking "+ ADD NEW", or (2) add a child component type by clicking a (+) button in the hierarchy.
Change the look of your components on the right side.
When you are finished, just exit by clicking on the x at the top right corner and everything is saved.