When you are developing custom extension which works with the ezcontentobject model you can assign different ez navigationparts with a section on a content subtree.
This is fine .

But if you want to have a different left_menu you have to modify the admin pagelayout.tpl to include your own menu tpl.

e.g ( ez default )
'ez content navigationpart' =>

{include uri='design:parts/content/menu.tpl'}

'ez customtext navigationpart' =>

{include uri='design:parts/customtext/menu.tpl'}

I did a little enhancement, that will extract the tpl name for the custom navigationpart and include this template.

The $navigationpart.identifier variable is only available if you did not set the navigationpart in your custom extension in module.php. Therefore their is a switch. See attached patch for details.

I hope this little enhancement will be in ez core in the future. So it is easier to make custom extensions with admin interfacemodifications.

Thank's
Best regards Felix Woldt