Does the reward for remembrance cease if the one remembering forgets a word or replaces it with another, such as changing "O Allah, I seek refuge in You" to "O Lord, I seek refuge in You," or omitting the repetition of "I seek refuge in You," not due to a failure in memorization but due to forgetfulness?

Firstly, it is best to recite the prescribed remembrances (adhkar) and supplications (du'as) with their exact wording, and not intentionally omit anything from them. However, if an omission occurs due to forgetfulness or error, there is no blame, for the Messenger of Allah, peace and blessings be upon him, said: "Indeed, Allah has pardoned for my nation their mistakes, their forgetfulness, and what they are forced to do." Therefore, not repeating what was meant to be repeated, or replacing the word "Allahumma" (O Allah) with "Ya Rabb" (O Lord), carries no blame, Allah willing.