Bazan on "custom nav_menu_item function"

Hello,

I have a CPT with a custom field called: special - yes/no value.

I want to do a custom nav menu item, that i can add item with text:
"Special product", which dynamically add url by find the only one post have a custom field special value on "Yes".

So if i change a custom field in products, i want that link in menu change, with no changes in admin's menu confugration.

Is it possible to define my own item like "SPECIAL PRODUCT" and set this link a dynamic link produced in some function?

I hope I explained it enough :P

I just want to change item link without change it in menu configuration, but by changing CPT custom value :)