There is a minhag to say at the end of Shemoneh Esrei and Kaddish during the 10 days of teshuva, "oseh hashalom" instead of "oseh shalom". This is mentioned in the Mateh Ephraim in Siman 582 as well ...
When a person says "HaKel HaKodesh" instead of "HaMelech HaKodesh" during Eseres Yamei Teshuva the halacha is they must go back to the beginning of the tefillah and start over again. What would be ...
What should be done in a case where the shliach tzibbur when davening chazaras ha'shatz makes a mistake and instead of saying "HaMelech HaKodesh" during Eseres Yamei Teshuva he says "HaKel HaKodesh". ...