Nikorima's switch to the Dragons on a two-year deal from 2027 was confirmed by both clubs on Wednesday ahead of their clash in Wollongong on Friday night.
The Dolphins will welcome England five-eighth George Williams, who played with Canberra previously, from Warrington in 2027 on a two-year deal.
The loss of the 32-year-old New Zealand international, who has been a standout performer for the Dolphins, will come as a shock to fans but salary cap constraints have prevented the club from extending Nikorima's time beyond 2026.
The Dolphins had seven players involved in the State of Origin series and several of them will be extended and upgraded.
Nikorima has said publicly his preference was to stay at the Dolphins, but his lucrative deal at the Dragons could be his last in the NRL and he has made it count.
Utility Schneider, who has been filling in at halfback for injured co-captain Isaiya Katoa, is set for an extension. The former Penrith representative will not be as big an imposition on the club's cap space.
Dolphins coach Kristian Woolf said the club tried to keep Nikorima, who had transformed himself from a utility player to one of the form starting five-eighths at the Dolphins.
"While I am sad to see him leave I understand the circumstances," Woolf said.
"He has been able to put himself in a position at the back-end of his career that he gets to maximise the efforts he has put in over the last four years with us.
"We were keen to keep Kodi. We made that clear all along. At some stage of his career he has to do what is best for his family as well.
"That's part of the game and part of our role at times, to help him get to that position."
Schneider, who was named at half in Katoa's absence against the Dragons, is in negotiations with the Dolphins for an extension.
Woolf said Schneider had played hooker, lock, five-eighth, half and off the bench for the Dolphins and brought a tough mindset.
"I have been really impressed with Brad," Woolf said.
"I love his versatility and influence on the group. He has come from a winning environment and he has brought that mentality to us."
"He is a guy we would like to keep around a bit longer."
Woolf said Katoa would likely miss the clash with the Dragons as he makes his way back from a broken wrist.
He was named in the No.22 jumper and flew out of Brisbane with the team on Wednesday, but is set to spend the match in the coach's box alongside Woolf.
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