How to change the style of a NSMenuItem ?

I don't any Cocoa's metod to change the style (bold, italic, etc.) of a menu item ?

MenuRef _NSGetCarbonMenu(NSMenu* aMenu);
By getting hands on the underlaying MenuRef, you have now access to the Carbon interface and may use every carbon routine:
OSStatus SetMenuFont (MenuRef menu, SInt16 inFontID, UInt16 inFontSize);
void SetItemIcon (MenuRef theMenu, short item, short iconIndex);
void SetItemStyle (MenuRef theMenu, short item, StyleParameter chStyle);
Apple Documentation for more info.
here is none, but there is an undocumented entry point in the AppKit framework: