The ARLC's February change lets players represent any country while keeping NSW or Queensland State of Origin eligibility.
Previously, Origin players could not represent New Zealand or England.
That enabled 35-year-old Queenslander Dane Gagai to switch allegiance to New Zealand through his mother.
He last played for Australia eight years ago and won the 2017 World Cup with the Kangaroos, nine years ago.
"I'll be doing everything I can to bring back a World Cup for New Zealand," Gagai said.
He described his heritage this way: "But being Kiwi for me isn't just where you're born and raised, it's who you are."
The 340-game NRL veteran has represented Australia, Queensland, Maori All Stars and Indigenous All Stars, but has yet to play for the Kiwis.
New Zealand opens against Australia in Sydney on Thursday night, with Gagai potentially facing Latrell Mitchell after Newcastle eliminated South Sydney from the finals.