Catholicism isn’t like other Christian sects where you can kinda interpret things your own way. The defining characteristic of the Catholic Church is a rigid adherence to established doctrine.

If there were somebody out there that didn’t hold confession to the standard that I do, they probably wouldn’t bother going to confession. It’s not something you’re forced to do at regular intervals. Either this hypothetical person believes in the sanctity of confession or they don’t. If they do, they aren’t going to go to confession to tell the priest that they aren’t sorry and are ready to offend again. And if they don’t, there’s no reason for them to go in the first place.

The only possible third option which is extremely unlikely, is somebody who doesn’t believe in the sanctity of confession, going into a confessional just to not confess at all but boast about their crimes and willingness to do it again. But in that case, they aren’t taking the sacrament, so the priest could report them.