Bruce Metzger observes that OUPW in Jn 7:8 "was introduced at an early date (it is attested by P66, 75) in order to alleviate the inconsistency between ver. 8 and ver. 10" (A Textual Commentary). However Ernst Haenchen (in his commentary on John) seems to think that OUPW is original. He reasons: "If Jesus does not know when his time is fulfilled and the Father calls him to Jerusalem (to die?) then logically he cannot say 'not,' but must say, as in v 6, 'not yet.' "
Even if OUK is not original, and we cannot be positively sure about its status, John's possible use of OUK does not mean that Jesus lied. A.T. Robertson points out that Jesus "did not change his plans . . . He simply refused to fall in with his brothers' sneering proposal for a grand Messianic procession with the caravan on the way to the feast" (Word Pictures in the NT).
Another scholar also makes this observation: "the more definite--and more difficult--reading, 'I am not going,' is undoubtedly the correct one. Jesus is represented as clearly refusing his brothers' proposal. He will not go to this festival at their request or initiative but only as his Father directs" (J.R. Michaels, John, 127).
C. K. Barrett writes: "He refuses in the plainest terms to comply with human--and unbelieving--advice, acting with complete freedom and independence with regard to men, but in complete obedience to his Father" (Barrett, John, 313).
Finally, we have these words from George Beasley-Murray: "That Jesus eventually goes to the festival EN KRUPTWi is to be interpreted strictly in relation to [John 7:4]: he journeys quietly to Jerusalem, without making any ostentatious entry into the city or drawing attention to himself on arrival at the festival" (Murray, John 107).