FTR, while the pull request has landed (automatically closing the GitHub issue), I think this hasn’t been deployed to production yet (perhaps not even to beta). I imagine, though, in the next few days?
You’ll be able to tell when it has deployed because the “Ladder card” in the group page will say “Rules: name-of-ruleset” above the list of ladders. For example, here is a screenshot from my testing:
When it deploys, all groups will initially say “Rules: Japanese”, since that’s still the default of course. To change it, a group admin needs to click the usual “edit” button, and the rules setting becomes a drop-down menu:
