What is meant by "changing the wording" in the author's statement: "And whoever errs in recitation with a word not from the Qur'an, he prostrates after the salām; but if it is from the Qur'an, there is no prostration upon him, unless the wording changes, or the meaning becomes corrupted, in which case he prostrates after the salām"? And does "changing the wording" include omitting a letter or pronouncing a letter between two letters, as happens with a non-Arab when reciting the word "qāla" (قال) with a letter between the qāf (ق) and the kāf (ك)?

The term "word" refers to the Quranic word. Changing it includes omission, addition, or substituting a letter. Whoever does so intentionally invalidates their prayer. However, for those who find it difficult, such as a non-Arab or someone with a speech impediment, they are excused as long as they cannot correct it, and their prayer is valid, as is the prayer of those behind them, if they are unable to learn or distinguish between letters that are difficult to differentiate. But if they are able to correct it and do not, then their prayer is not valid, nor is the prayer of those who pray behind them.