How can i mark menuitem in Application Bar. I want to get, for example, this:

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I’d say it can’t be done. The menu items are just calls to functions and can do nothing but show the corresponding text and call the corresponding method when activated. I’ve found some examples of people hacking extra functionality into them (updating the text or changing the function calls, to some extent), but nothing beyond that would be possible.
Notice that what you can do with the AppBar is limited by the functionality offered by IApplicationBar and, in your case, ApplicationBarMenuItem. And none of them expose anything even close to your requirements.
You can, however, enable and disable menu items, although I don’t think that’s what you want.