But he can't. All he can do, if he's against a doctrine, is to neglect it, obfuscate it, undermine it, or violate it. But he can't change it. Because he hasn't the authority.
You apparently understand neither the severe limitations where papal infallibility is in effect nor the broad definition of Catholic doctrine as described in the Catholic Encyclopedia.
Finally, it is you, not I, who describes herself as a papist on her home page.