A word can have a few shades of meanings depending on the context, the usage, the sentence, etc.
Today's feast is called the Conversion of St. Paul.
What is generally understood is that St. Paul converted from being a persecutor of Christianity to become a missionary for Christ and an Apostle to the Gentiles.
The conversion is not from one faith to another. Rather the conversion as understood in the life of St. Paul is an enlightenment and a clarification of his understanding of God and who Jesus really is.
This feast also reminds us that no conversion is impossible because God wants all to be saved.
If St. Paul can turn from being a persecutor of Christianity to a proclaimer of the Good News, then there is certainly hope for those so-called hardcore sinners.
May we ourselves be converted to believe that God is truly merciful, compassionate and forgiving.
And may we not judge those who do evil. Rather we must pray for them for Jesus wants to save them too.