Only On Yom Kippur You Are Allowed

According to the Magen Avraham & MishnaVerurah. (565) 

There is only one day in the year (YomKippur) that 

the Piyut האדרת והאמונה ,לחי עולמים  may be said בציבור 

In Nusach Sfard (Ari)  it is said every Shabbos. 

They don't follow this Psak of the  Magen Avraham/M.V.

Nusach Ashkenaz says it only on Yom Kippur

There are two* more things that are allowed to be done 

only on Yom Kippur and not the rest of the year.

1) Standing up for קריאת שמע.

2) Saying י"ג מדות & סליחות in the night time before חצות

*that I could think of.- Saying aloud  בשכמל"ו is done also during the year.