Is Interference from the Prophet in Wahy Possible?

The deniers who believed that the Quran was not the word of Allah, but something made up by Prophet Muhammad (pbuh), regarded the Holy Book as a human creation that could be altered as one wished and they thought the ayahs they did not like could easily be replaced with ayahs they liked or wanted. In particular, they did not want the Quran to speak of the gods and idols they worshipped and associated as partners in the attributes of Allah. For this reason, some of them asked the Prophet for another sort of Quran or they proposed that he alter the wahy which he had received up until then.

 Upon this request, Allah revealed the following verses: "And when Our clear communications are recited to them, those who hope not for Our meeting say: Bring a Quran other than this or change it. Say: It does not beseem me that I should change it of myself; I follow naught but what is revealed to me; surely I fear, if I disobey my Lord, the punishment of a mighty day."  

For Prophet Muhammad, a man who acted with utmost honor, even the possibility that his sayings could be mistaken for verses from the Quran was a serious concern; he would not have even considered altering a verse or making up one as he wished.