Complex sentence: Feel free to change it--within reason--if you think a different rating is justified; in the case of major disputes, the WikiProject as a whole can discuss the issue and come to a consensus as to the best rating.
Split into simpler sentences: Feel free to change it--within reason--if you think a different rating is justified. In the case of major disputes, the WikiProject as a whole can discuss the issue and come to a consensus as to the best rating.