The three faiths referenced have some significant differences. There is a fairly sizable number of atheists who consider themselves "culturally" Jewish, and there's a certain extent to which the religion focuses more on behaviors than beliefs. There are also people who consider themselves "non-theistic" Christians --followers of Jesus as conceptualized as a purely human rather than divine teacher. The mainstream Christian church, however, definitely does not accept such people as actual Christians. "Non-theistic Islam," on the other hand, doesn't even make sense as a theoretical concept.
With that said, when each religion is considered in its core, theistic form, each presupposes the existence of God as foundational. It's hard to see any way clear to make a statement of the form "I don't think I'm justified in believing in God, but I do think I'm justified in believing that the religion of Christianity is right."
It might be the case, however, that a specific religion conceptualizes God in such a way that there is new and better evidence for that view of God than for the more general one you previously rejected. For instance, Kierkegaard's existential Christianity embraces the absurd. When considering God in the abstract, you might take certain perceived absurdities as counter-evidence. If you came to embrace Kierkegaard's perspective, however, you might no longer find that counter-evidence decisive.