It does not permit the individual to by-pass the RCIA on his own authority - you can’t walk up to your priest and say, “I have chosen to by-pass the RCiA.”
But if, after the initial interview, the priest discerns that you don’t need RCIA, then he can permit you to enter the Church more quickly, through a means of his choosing, such as private instruction, or an arrangement where you send him an e-mail once a week for so many weeks, on a list of topics that he gives to you, or whatever other arrangement he decides to make for you.
Most people go through RCIA, because most of us are not at the genius level of someone like Scott Hahn - there are occasionally people who can bypass the RCIA, that the priest will work with in a different way, but most of the time, they will send you to RCIA.
In the case of the Catechumens of the first century, if they failed to complete their RCIA process (which at that time was between three and seven years, depending on the Diocese) they would receive Baptism of Blood (if they died in the service of Christ) or Baptism of Desire (if they died of an illness or accident) - God will give you whatever you lack, as long as you are doing everything possible for you to do here on the earth.
There are no tests or anything like that. It’s you, discerning for yourself. For example, I had a lady in an RCIA class one time who was only coming because she had to - she was convinced in her own mind that she knew everything and was ready to become a Catholic right this minute if not sooner, but the priest told her to take RCIA, and she was being obedient to him.
Over time, as she studied the teachings of the faith with us, she discovered things she hadn’t known about, such as the requirement of Sunday Mass, the requirement to go to Confession, the laws of fasting, and so on, and at that point she decided that the Church was too “legalistic” (her word) for her tastes, and she decided not to become a Catholic.
Now, what would have happened to this poor lady if she had been allowed to become Catholic at the moment that she said, “I know that I am ready”? She would have made a life choice for something she did not yet know, and taken on obligations that she was unwilling to fulfill - and she wouldn’t have found out about them until
after she had made her vows - too late.
The Church actually did her a favour by “making” her wait, because in the end she realized that she was not able to obey the commandments of the Church - and by never having made a vow to do so, she remains in God’s good graces - you cannot be found guilty of breaking a command that was never given to you, after all.
Maybe some day she will be able to become a Catholic, but when she does, she will have a clear idea of the commitment that she is making - there won’t be anything to catch her off guard.
The purpose of the four periods of discernment in RCIA is so that you can have the time to examine the Church, and see whether you can fulfill what the Church requires of you. It’s not for other people to examine you, or test you, or keep you out. No one will ever do that. On the last day, they will ask you, "Are you ready to take up the life of a Catholic?’ and it will be your answer - “Yes, I am,” or “No, I am not,” that will determine whether you receive the Sacraments that night. No one else will speak for you, or judge you - you will only judge yourself.
