You seem to be referring to the sin of “presumption”…in other words, when people believe they can committ a sin and just go to confession.
Those who err this way amplify their sin and add another. God has not heard of “double jeopardy” as defined in our Constitution.
If you run into someone who comments about this (ie: don’t arbitrarily condemn them…let them bring the topic up), define presumption to them and help them understand that they will not be absolved.
The priest will act in good faith (unless he is like a priest I know who has the charism of reading hearts–he actually didn’t absolve me once but told me to come back). Anyway, the priest will act in good faith and absolve the penitent, however, God knows what is really in the heart of the person.
In order to be absolved, we have to be truly sorry for our sins and have a FIRM PURPOSE OF AMENDMENT. Now, if your friend is committing a mortal sin knowingly and does honestly feel sorry for it later, but had at the time of commission considered Confession as an “out”, then he/she needs to also confess the sin of presumption.
Hopefully that made sense. It is late and I should really be sleeping.