Does internal monologue affect the intention of worship, such as when a worshiper speaks to himself about changing the intention of the prayer, thereby invalidating his prayer, or like someone who intended to pray Asr then spoke to himself about intending to pray Isha while on his way to the mosque, so are his intention and his prayer valid?

Updating one's intention during or before prayer does not affect it, as one is not held accountable for inner thoughts. Hesitation to break the intention of prayer does not affect it, unlike outright rejection. However, intending to pray before reaching the mosque is not sufficient, for the intention must coincide with the takbīrat al-iḥrām (the opening Allahu Akbar) or precede it by a very short time. One must be wary of whisperings (waswas) and turn away from them.