One path alias for differents / multiple internal path? The problem is when a menu item points to a restricted page, the anonymous user can't see the menu link.

So I was looking for a way to setup a path alias so it would point to two internal path => one for anonymous and one for logged users.

Is this solution possible? Do you see another way to show restricted menu item to guests ?
You cannot have one alias for two items. That's not how router works. On the other side, you can create a page only guests will have permission to see, and place it under the same name in the same menu. Then both guests and logged in users will see identical menu, but they will actually get different set of menu items.

If that's not enough, you can use Menu per Role to get more control of who sees what in your menus.