I imagine that your son doesn't want it to stop either. Perhaps a roleplaying exercise (or just a discussion) about the implications and possible results of swearing at school would be in order?

Although it sounds like he does not plan to swear at school, and believes he has enough control not to let a swearword slip out. In which case it might be best to leave 'swearing at school' on the table unless he actually does it, in which case a lesson on contrition might be in order.

Swearing at home is a harder problem, I fear, if there's no clear and articulable reason why he ought not. Although I see you mention words that are "attacks on groups", which makes it sound like he's using slurs; if that's the case, I would suggest that a broader, serious talk about the historical context of them is in order. I expect he is plenty capable of understanding it. (But in explaining that, you will probably want to concede that some words are much worse than others, even in the realm of "things we'd prefer you didn't say at home.")