Charles announced his involvement in the competition at The Hills clubhouse yesterday, while New Zealand Golf tried to verify whether the tournament would be his 46th or 47th Open.
The March 12-15 event will be the first New Zealand Open co-sanctioned by the Australasian Tour and the United States-based Nationwide Tour.
New Zealand Golf invited the country's greatest golfer to play, assuring him he would not be taking the place of a younger professional by competing.
Speaking to the Otago Daily Times, Charles said despite being of an age where all other New Zealand Open competitors were young enough to be his son, his game had not deteriorated in the 15 months since he stunned the competition in 2007.
"It seems a bit ridiculous but life has been good to me. From a competitive point of view my game is untested, but in general I'm hitting the ball just as well as I was 15 months ago," he said.
A surprise entrant in 2007 after retiring in 2004, Charles became the success story of the first Open played at The Hills, finishing tied for 23rd and the third best New Zealand competitor behind Josh Geary and Gareth Paddison.
He twice beat his then-age (71) with a 68 in the second round and a 70 in the final round, and is out to better his own record this year.
"If I don't shoot my age or better, I feel like shooting myself," he joked.
He will celebrate his 73rd birthday during the tournament.
Charles recently shot 72 off the back tees at both Clearwater and Millbrook, although when asked whether he felt confident going into the Open, he said he was prepared for a poor performance.
"I've never been a particularly confident player. I'm hopeful of a good performance but by the same token, I won't be at all disappointed if I fail miserably because I don't have any expectations, which was the same 15 months ago."
He said the quality of golf should be better than in 2007, when the Open ran in conjunction with a European tour and very few high-end players made the journey to New Zealand.
"That was the only disappointment of the tournament. This year we will have the best of the Nationwide Tour players, mainly Americans, and for that reason the quality and competitive element of the tour will be better than it was."
He will not compete in the first two tournaments of the tour, which will be held in Melbourne and Christchurch, although he plans to watch the first two days of the New Zealand PGA at Clearwater before making his way to Arrowtown.
Charles' success in 2007 was attributed to warm weather and thorough preparation, the latter of which would be lacking this year, he said, as spare time was scarce.
Temperatures above 15degC are on his March wish list.
"I am playing one round a week, and spend an hour hitting balls every other day. It's no secret that the better the weather the better I play . . . my performance deteriorates rapidly in cold weather," he said.
Charles played five tournaments in the United States and seven in Europe during 2008, and plans to play another six this year following the New Zealand Open.
A function at The Hills had been planned to celebrate Charles' induction into the World Golf Hall of Fame last year, before it was known his birthday would be on the same date.
He said his performance in this year's Open would have some bearing on whether it was his last professional tournament.
"The only thing that would put an end to my competitive golfing career would be if I embarrassed myself with scores in the 80s," he said.
