"I'm clear in my mind that I'm finished with them," Nicholson said. "I have drawn a line and will carry on doing my own thing. They forget I've been doing that for seven to eight months anyway."
Efforts by Nicholson to solve the problem through High Performance Sport New Zealand also proved unresponsive.
"I think I'll stick to my own shovel and do my own digging," Nicholson said of their efforts.
ESNZ received $2.05 million of taxpayer high performance funding last year and are scheduled to receive $7.45 million across the 2013-16 cycle, the fifth-highest of any New Zealand sport.
Part of that investment was based on Nicholson's performances. He helped New Zealand win team bronze at the 2010 WEGs and 2012 Olympics.
Nicholson wanted to compete for New Zealand at next month's three-star Aachen event but ESNZ could not get him an entry.
"There are limited entries, they only want the top riders," the world No.4 said.
"Most countries can only have a team of four riders but New Zealand is one of a few allowed an individual as well as team of four.
"I'm the only New Zealander to win there [in 2010 on Nereo after eventing became part of the competition in 2007].
"They decided it's too soon for me to be integrated back into the system, so why were they wanting me back on the high performance squad?"
ESNZ chief executive Vicki Glynn believed it would take a few months for him to reintegrate with a new squad.
"He made it a condition he would be on the team for Aachen. We felt that would be inappropriate.
"As for the end of his Olympic career, well, we don't see it like that. The selectors can exercise discretion [and bring him back into the squad]. We would encourage him to send in his [Olympic] application by the deadline of July 25. There's no barrier to him doing that.
"He just needs to sign an athlete agreement which most sports have [between athlete and governing body]. That's the only thing that needs to be agreed for him to come back.
"We appreciate after what has happened that there might be special circumstances, which we're prepared to amend to meet his needs, but we never got to that in the discussions. Once we struck the Aachen situation, he withdrew."
Nicholson said he was faced with a moral dilemma.
"The main reason I originally took myself off the programme was because I wouldn't have been happy taking taxpayer funding as a high performance athlete and not being able to represent my country. So what has changed?
"I wouldn't mind if they had said 'you're not good enough', but 'too soon to be re-integrated'; that's the biggest load of rubbish.
"They might have this over me as a bit of an ego trip, but who do you want at these big events: a Porsche or a Morris Minor?
"They say other riders are not comfortable working with me, but I find that hard to believe."
Complicating matters is the fact New Zealand are yet to qualify for any spots at Rio after their 15th-placed team performance at the WEGs, site of the original fall out. Only the top six and host country Brazil automatically qualified.
New Zealand must contest an Asia-Pacific Olympic qualifier in the Netherlands in October when Japan are expected to be their main competitors. Fail, and they will have to qualify a composite team via the individual world rankings.
However, with three scores counting out of four riders at Rio rather than five riders at London, the emphasis will be on athletes suited to a team, because that's perceived as New Zealand's best chance of earning one of two targeted medals.
Jock Paget, Tim and Jonelle Price and Sir Mark Todd have secured top-10 finishes at four-star events in the past year. Those four, along with Caroline Powell, Lucy Jackson and Clarke Johnstone, are in the current HP squad.
"If there were five riders at Rio, you could have someone on a more individualist pathway, but if three out of four scores count, you have to work to a team strategy," Glynn told the Herald on Sunday in May.
"Andrew's a reliable individual but it can't be at any cost. We can't let him determine his own fate, ride at his own pace and not follow a collective decision.
"Andrew has been a great team player in the past, there's no reason he shouldn't be again."
"If I'm good enough and needed for Rio, it'll be on my terms," Nicholson said. "The Olympics are not until next year. They could change their attitude if the main players run out of horses."
