Does intentionally prolonging the pronunciation of the letter "mim" in "Al-Hamd" or the letter "lam" in "liman hamidahu" affect the validity of the prayer?

If the letter "Mīm" in "al-Hamd" is intentionally repeated, and the meaning changes, the prayer becomes invalid. However, if the repetition is merely an elongation of the "Mīm" sound and an extension of the ghunnah (nasal sound), the prayer is not invalidated, though it is a لحن (lament/mistake) that should not be done intentionally. The prayer is also not invalidated if the error is merely due to whispering (waswasah).