I'll add here, criminal law is typically within the purview of the States to enact and enforce. There are of course federal crimes, most notably the Unlawful Inclosures [sic] Act, which makes it illegal to block a corner from public access. As this is the only law on the books that directly deals with corner crossing, logic would dictate that corner crossing is already federally legal. This was a significant part of the 10th circuit's ruling.
@Eric Albus Corner crossing doesn't need to be "legalized" because it has never been made illegal in Montana in the first place. As much as our Gov Lt. Gov., and FWP director would like to will that into existence. As
@DP_PublicLands also rightfully pointed out, SCOTUS doesn't have to and likely won't take up the issue. To that end,
@BuzzH SCOTUS declining to take up the issue doesn't mean they have made a ruling, it just means they don't care enough to resolve it for anywhere outside of the 10th circuit.