Changing a letter during recitation in salaah

Q: I read in a book that if you change a letter during recitation in salaah, the salaah is broken. Such as reading the letter ت instead of  د such as at the end of Surah al Falaq reading HASET instead of HASED. But somehow when I recite HASED no matter how much I pay attention to recite it with D I hear a T sound at the end coming out. Does this still break salaah? To break salaah does it need to change meaning, if HASED is read as HASET does it change meaning?

Memorising the Qur'an

Q: Could the following be verified with a source please:

  1. While memorizing the Holy Quran, If a person passes away the Angels of the grave will assist him in completion.
  2. The place on the body which received hiding while doing hifz will not be burnt in the fire of Hell.