How to remove a Navigator item from the "Core" layer, using the Navigator from the "Cust" layer?

Hello, I work with IFSAPP10 and Visual Studio, and I need to remove 1 Navigator menu item that belongs to the Core layer.
 

As I only have permission to use the "Cust" layer, I open the Navigator editor, click with the RMB on the item and the "Remove entry" option is disabled. See below:

Okay, I believe this happens because I'm using the "Cust" layer project and the item originally belongs to the "Core" layer project.
 

Does anyone know how I can delete this item through the Cust layer? would it be possible to do an "overtake" or "override" in the "Core" layer of the Navigator? How can I do this?

Thanks in advance for any help!