bool IsConverter(string alias);

public bool IsConverter(string alias)
{
    return alias.InvariantEquals("rte");
}

IEnterspeedProperty Convert(GridControl editor, string culture)

public IEnterspeedProperty Convert(GridControl editor, string culture)
{
    return new StringEnterspeedProperty(editor.Value.ToString());
}

public class MyCustomerGridEditorValueConverterComposer : IComposer
{
    public void Compose(IUmbracoBuilder builder)
    {
        builder.EnterspeedGridEditorValueConverters()
            .Append<MyCustomGridEditorValueConverter>();
    }
}

[RuntimeLevel(MinLevel = RuntimeLevel.Run)]
public class MyCustomerGridEditorValueConverterComposer : IUserComposer
{
    composition.EnterspeedGridEditorValueConverters()
                .Append<MyCustomGridEditorValueConverter>();
}

public class MyCustomerPropertyValueConverterComposer : IComposer
{
    public void Compose(IUmbracoBuilder builder)
    {
        builder.EnterspeedGridEditorValueConverters()
            .InsertBefore<DefaultRichTextEditorGridEditorValueConverter, MyCustomGridEditorValueConverter>();
    }
}

[RuntimeLevel(MinLevel = RuntimeLevel.Run)]
public class MyCustomerPropertyValueConverterComposer : IUserComposer
{
    composition.EnterspeedGridEditorValueConverters()
                .InsertBefore<DefaultRichTextEditorGridEditorValueConverter, MyCustomGridEditorValueConverter>();
}