Right... so you hold that a Catholic who becomes a heretic, is still a Catholic. So then you would logically have to conclude that Martin Luther remained a Catholic when he became a heretic, he's just a "Catholic in mortal sin" according to you, right? Clearly, you reject the Unity of the Church. It's a dogma that the Church is one in Faith. You reject that. You are not a Catholic.
Have you figured out which of the Divine Laws is being broken by having a heretical pope yet? Or will you just keep ignoring the question?
"Thou art a priest forever according to the Order of Melchizedek." Ever heard of this?
Luther stood before God as a Catholic priest in the state of (as far as we know) mortal sin. The sin you refer to is a sin against the faith, i.e. the sin of heresy.
The character of the sacrament of baptism is just as indelible, just as ineradicable as that of Holy Orders. One who is not a Catholic cannot receive the Sacraments. The Catholic who has fallen into the sin of heresy can receive the Sacrament of Penance.