I tend to think it's not black & white to the point whereas if one questions it's accuracy that it puts one outside the Church. The exception to the rule is that if one is teaching while representing the Church, such as a priest or a teacher in the RCIA program, they must teach the Trinity as accepted and taught by the Church.
Yes, as priest or catechist one is speaking with the authority of the Church. We all have questions and opinions as do the Church's own theologians.
I have many of my own on positions of the Church; homosexuality, birth control, the ordination of women etc., I am only speaking of 'core' beliefs, not the formulation which as dogma is open to development.