I'm not sure how "legal it is" but there are adapters available to modify the propane "left hand thread connectors" to the newer style. They are available several places, and as usual, Amazon tops the list:
https://www.amazon.com/Hooshing-Prop...a-833008127270
There was also a 20% limiting valve that was added some time ago, and I'm not sure if or when that was grandfathered into recertifications, or if it ever was.