Mispronunciation during Keria:
If the Baal Korei mispronounced a letter or word, then the Ashkenazi custom is that if it changes the meaning of the word, he must repeat it. If it does not change the meaning of the word, he is not to repeat it. The same applies if he read the word in the wrong Niggun, he is not required to repeat it. Nonetheless, he is to be reprimanded. [Practically, some are accustomed to go back and repeat it even for a slight mispronunciation or change of Niggun, and so was the custom of the Alter Rebbe. If the Baal Korei read the Kesiv instead of the Keri he is to be corrected.
 Rama 142:1; Ketzos Hashulchan 84:9; See Admur 64:2
 Sefer Hasichos 5696 p. 52
 See Michaber 141:8