@Chris_Wilmore St. Peter had the graces of the Holy Ghost as an Apostle. Nobody has those graces today. It would take years of training. I am too old to even begin seminary.
Those things can generally remain after conversion to Christianity! The shrines would be re-dedicated to a saint and offer worship the true God. They would have to stop with superstitions like charms and fortune telling, but those can be substituted with indulgences (though fees are banned due to Middle Ages abuses), perpetual adoration, relics of the saints, etc.