The decision is Whakatōhea Kotahitanga Waka (Edwards) & Ors v Te Kāhui and Whakatōhea Māori Trust Board & Ors, and it basically reinterpreted section 58 of National's Marine and Coastal Area (Takutai Moana) Act to make it consistent with its purpose clause and te Tiriti o Waitangi by allowing "shared exclusivity" according to tikanga. The upshot is that it would become significantly easier for iwi and hapū to gain customary marine title over their foresore and seabed - a fact confirmed in subsequent court decisions. National doesn't want that to happen - in fact, they don't want Māori to be able to gain customary title at all, despite what they promised Te Pāti Māori when they passed the law in 2011 - and so they plan to legislate it away (which they disguise as "restoring the intent of Parliament" - which is effectively an admission that they dealt in bad faith with their coalition partner in 2011). Of course, they're pitching this as being about beach access, like they always have, even though that is not and never was under threat. But they're quite open in the Herald about what its really about: protecting the aquaculture industry. So Māori rights are going to be sacrificed to protect National's donors and cronies. Which sounds just a little corrupt.
As with the 2004 law, no-one should expect Māori to take this lying down. And in the context of National's other attacks on Māori - the repeal of s7AA of the Oranga Tamariki Act, the attempted eradication of te reo from government, their plans to repeal / "reinterpret" te Tiriti - it is likely to lead to significant protest. And as with those other issues, no matter what "solution" National comes up with, it will be reversed by the next government, in the same way that Labour's Foreshore and Seabed Act was. The question then is how many aquaculture consents they will have corruptly given out in the meantime, and what will be done about them and the corporate scum who have corruptly instigated this mess.