There is a custom to eat apples on Shabbat, as well as saying (Hakal Tapuchin) "apple field Kaddishin". On Shabbat that falls on Yom Tov, as well as on Shabbat that falls on Rosh Hashanah, do we establish this custom, and also do we say the parts in Aramaic that mention "Hakal Tapuchin Kaddishin"? Are there any Shabbat that this custom is not applicable?