"Should you address poor law school grades in a resume and if so, how?" No, do not even talk about bad grades. Just pretend like it didn't happen, get in the door, get liked, if people ask you about your grades later on, that's fine. Honestly, the biggest firms and the most prestigious firms take grades seriously when you're in law school, or when you're coming out of law school, and your first three years, but after that they generally don't matter except for a few firms. And in addition to grades not mattering, the majority of firms are not large firms, the majority of them are smaller firms.
So those firms also typically don't care about your grades. Just don't even put anything to do with them in your resume. And honestly, grades do not matter. Some of the best attorneys out there had bad grades in law school. There's nothing you need to really go into detail. Practicing law, certainly grades are important, but it's not the most important thing.