Townley will take the place of injured Honda star Chad Reed for TwoTwo Motorsport when the United States champs begin at Hangtown, near Sacramento, California in May.
Townley's domestic campaign began with victory at the Whakatane Summercross just after Christmas followed by a NZ Grand Prix win at Woodville and a nationals blitz that brought 11 wins and one second place - after a first corner spill - from 12 starts.
"Twelve out of 12 was there for the taking and it's a shame it didn't quite work out. But I have to say I'm now pretty close to the best form of my life, which was back in 2007," said Townley.
"Mentally and physically and with my riding I'm in a great spot right now."
The US campaign will see Townley and his young family relocate to Florida in the coming weeks rather than commuting to the Australian races from Tauranga.
"TwoTwo Motorsport is an amazing team and the chance to replace Chad is a once-in-a-lifetime opportunity," said Townley.
"The connections between TwoTwo Motorsport and Honda Australia all came together and I have their blessing to take this opportunity."
Meanwhile, Suzuki team-leader Cooper produced his best performance of the series with three second placings at Taupo and finished 23 points behind Coppins in the MX1 title race.
Three other BOP riders claimed MX1 top-10 rankings with Rotorua's Michael Phillips (Honda) finishing fifth, Rotorua's Brad Groombridge (Honda) seventh and Mt Maunganui's Mason Phillips (Kawasaki) eighth overall.
The battle in the MX2 series went to defending champ Darryll King (Hamilton). Two wins and a third at Taupo put King well clear of title rival Scott Columb (Queenstown) who was forced to retire with a smashed brake disc in the final race.
The big mover at Taupo was Papamoa's Rhys Carter (Suzuki) who raced to fourth in the opening moto and then scored his first win of the series in race two. Carter fought back from last spot after a crash at the start to claim 11th in the third moto and his final round effort moved him ahead of Tauranga's Peter Broxholme (Tauranga) to finish third overall. Broxholme went down in a first-lap crash in race one before recovering to 20th and then posted eighth and 10th to finish the series in fourth.
On the comeback trail from injury, Rotorua's John Phillips (Honda) showed impressive speed chasing King to a second place finish in the final moto and was sixth overall.
Amberley's Micah McGoldrick (KTM) continued to dominate the 125cc two-stroke class with three more wins, taking his tally for the series to 10 out of 12. McGoldrick won the title from Rotorua's Cameron Vaughan (Yamaha) and Te Puke's Logan Blackburn (Yamaha).
Blackburn, 17, was contesting senior nationals for the second time after finishing 10th last year and bettered his goal of a top-five finish by grabbing the final podium spot. He was fourth overall on Sunday, bouncing back from a spectacular spill in the opening moto when he finished eighth, before recording a fourth and a third.
Contesting the senior nationals for the first time, Katikati teenager Garth Amrein (Yamaha) posted a seventh, 10th and eighth at Taupo and finished the series eighth place.