public class TestOperation extends OperationContributor
{
    @Override
    public boolean contributesTo(Object target) {
        return truel;
    }

    public String getName() {
        return "MyTestName";
    }
}

EglFileGeneratingTemplateFactory factory new EglFileGeneratingTemplateFactory()
OperationContributorRegistry operationContributorRegistry = ((EglContext) factory.getContext()).getOperationContributorRegistry();
operationContributorRegistry.add(new TestOperaion());

context.copyInto(preprocessorModule.getContext());

• Did I use the correct method to define new (default) operations?
  
• If so, whether I found a bug that needs reporting or not?
  
• Should this be documented in the Epsilon book, as it seems nice to define global available user-defined operations
  

Import also accepts full plugin-based URIs so sharing code between different plugins shouldn't be a problem.

You're right regarding copyInto(). If you really need this I'll try to implement a quick fix for it otherwise I'm inclined to leave this until I'm back from holiday so that we can discuss with the rest of the team how we could get rid of copying contexts altogether (as hinted by the comment at line 170 of EglModule )