From what I know from the priests from the Greek Archdiocese here, unconfirmed converts who were originally baptized in the RC, are generally received through chrismation, confession and profession of Orthodox faith. And when the RC had been previously chrismated, proffession of faith is often enough, though unction with Holy Chrism is administered to, but differs from the full sacrament of chrismation.
And about "renouncing their errors", Bishops have called to have a criteria about each individual situation. The thing here is that not all the cases of conversions to Orthodoxy from the RC are that of the "convinced" RC who decides to become Orthodox only because he/she wants to marry an Orthodox, or because of a similar reason.
I don't think a person who was baptized in the Roman Church, but doesn't attend Catholic Mass for whatever reason (in many cases a reason of conscience which separates him from the hetherodox doctrines proffessed by that community and that mass, etc.), and is clearly out of that community, and then places himself in Orthodox services, and gradually becomes Orthodox, then the person would in essence not be a Catholic, de facto, in the first place, relying exclusively on the Orthodox Church for the sacraments, for community worship, etc.