That's why the deny concept was mostly removed, people misunderstood what it was. Basically you've got three 'states' of access: allowed, neutral, and denied. Denied always takes precedence over everything else, neutral will pass in an allow if the user has one along their access chain (otherwise it's denied), and allow is just as you think.
So to directly answer you question, no, you wouldn't need to delete the group and add it again. You'd just set the access back to neutral, which means that users don't have permission to it unless they get it from somewhere else.
The concept of denying is still available for users, but not on groups. This is in part because even if an admin misunderstands the differences between allowed, neutral, and denied, it will still act like they want it to at the user level. But, they can't screw up the group anymore because that option no longer exists. It doesn't really make sense to deny something to a group in the first place, so everyone's happy.