Is the statement "By God, if the Prophet (peace be upon him) were to come, I would not go with your belongings" considered disbelief, insult, degradation, or disparagement of the Prophet (peace be upon him), if said out of stubbornness to a brother and without the intention of insulting or disparaging?

This is a grave statement, and repentance is obligatory for it. Whoever says, "Even if the Prophet came to intercede for him, I would not accept it from him," commits an act of disbelief (kufr) and is to be killed unless he repents before he is apprehended. He disbelieves if he says it out of mockery or contempt. However, if he says it as an exaggeration to glorify the Messenger of Allah, peace and blessings be upon him, and not out of mockery, then he does not commit an act of disbelief.