I've heard that we are more lenient in regards to krias haMigglah than to krias haTorah (in regards to pronunciation), since the Migglah refers the itself as an Iggeres (letter). If this so, to what extent? [For example, if the baal koreh missed a ti'pcha, and instead read the pussok straight, do we require him to go back?] Please cites sources.
See Shulchan Aruch Orach Chaim 690:14 who brings two opinions. One that simply says that we don’t make a fuss about mistakes, and a yesh omrim which limits this to mistakes which don’t change the meaning.
So it would seem that according to both opinions, a mistake in the ta’amim would not be corrected.