mek42 wonders about attending a Catechism class : "I am currently a lapsed, non-practicing, unconfirmed Catholic… Assuming I remain so, would … [attending] catechism regarding Catholicism … increase my probable lack of grace (due to increasing knowledge [causing an increase in my responsibility to practice Catholicism] )?"
Since you do not believe in most tenets of Christianity (much less Catholicism), why are you considering attending a Catechism class?
This is perhaps the Most important thing.
Intentions are very important to determining if an action is a Sin.
So, look deeply into your Heart, and listen for the answer.
To address your question Head-on, nobody actually KNOWS for sure if attending a Catechism class is going to (somehow) increase any After-Life punishment.
Do you believe that you will go to Hell, if you do NOT have MORE Catholic Faith than you do now?
If your answer to this Question is “YES” … then you have little-or-Nothing to worry about.
If a person is going to Hell anyway, then how could doing something possibly-Bad, actually increase that problem?
So, in this instance, there is NO down-side to going back to Catechism classes (but this time, Catechism for Confirmation preparation).
However, attending Confirmation class brings up the NEXT issue:
Should you THEN become Confirmed as a Full-fledged Catholic? … Would THAT increase your Hell-risk?
But THAT is the subject of a future Thread … that is, IF you choose to attend Confirmation classes.