Is it possible to write a Mashriqi reading, exactly like the reading of Ibn Kathir, just as the Maghribi reading is like that of Al-Dani? Is there a text or a saying that prevents that? And what is the relationship betweenضبط (dabt) and قراءة (qira'ah)?

It is permissible to write any mutawatir (authentically transmitted) recitation in Maghrebi script, provided the calligrapher adheres to the Uthmani script, because the script is tawqifi (divinely ordained and unchangeable). As for the dabt (vocalization/diacritics), it is not tawqifi, and it is permissible to use either the Maghrebi or Mashriqi dabt, while adhering to the correct vocalization of the letters according to the reciter's pronunciation, as the dabt follows the recitation.