No, I'm pretty sure challenging the status quo is not an excamunicable offense. Members are entitled to oppose any callings or revelations and openly show it if they wish. - Now it does become an issue when people claim revelation and prophecy outside their stuwardship. For example, I can recieve revelation for myself personally to let me know important things like where I should work, where I should live or to relate the scriptures to myself so I can more fully understand them. But I couldn't recieve revelation for you that you should move to Detroit and become an Optician. - Or I may recieve revelation that it would be good for me to marry a certain young woman, but I can not recieve revelation for her that she ought to marry me. - Also I was recently a "Branch Missionleader" with that calling I was entitled to revelation regarding missionary work in the branch. But I couldn't go to the Relief Society President and tell her, "I've recieved revelation that you need to hold a finance workshop at your next Enrichment activity." - Doctrine and Covenants 28 deals with this somewhat, the introduction says: "Hiram Page, a member of the Church, had a certain stone, and professed to be receiving revelations by its aid concerning the upbuilding of Zion and the order of the Church. Several members had been deceived by these claims, and even Oliver Cowdery was wrongly influenced thereby. Just prior to an appointed conference, the Prophet inquired earnestly of the Lord concerning the matter, and this revelation followed. " - Hiram did not have authority to recieve the revelations he claimed. - This section also sets forth a pattern that only the President of the Church will recieve new commandments and that nothing will "be appointed unto any of this church contrary to the church covenants." D&C 28:12

There is only one Prophet at a time authorized to speak for God in our age. This is a pattern established by God. Any other claiming to speak for God as a prophet is, by definition, not loyal.