Is it permissible to intentionally recite "al-Zarat al-Mustaqim" instead of "al-Sirat al-Mustaqim" in al-Fatiha during a loud prayer, and is this recitation valid?

The reading of ishmam of the letter sad as zay in the word (الصراط - As-Sirat) is an authentic and consecutively transmitted recitation (qira'ah mutawatirah). This is the reading of Hamzah Al-Kufi, one of the seven reciters. It is permissible to recite with it in prayer and otherwise, and to teach it to people. However, the reciter or Imam should not confuse the common people with a reading unfamiliar to them, especially in prayer, lest it lead to distraction from khushu' (devotional humility) or doubt about the correctness of the recitation. Imams and reciters are advised to hold study circles to teach the recitations in order to spread knowledge about them, and to avoid reciting with the unfamiliar when leading people in prayer.