United announced the 119-year-old venue is to now be called the Sports Direct Arena - named after owner Mike Ashley's retail company - until a permanent sponsor can be found.
The club claim the move is necessary as it will allow them to generate extra income, but former England cricketer Harmison believes it carries the same sentiment as adopting the colours of arch-rivals Sunderland.
Writing in the Daily Telegraph, he said: "I can only liken it to changing the team's colours from black and white to red and white and making us look like Sunderland.
"That's how big a deal it is. You do wonder whether they would do that if the money was right.
"St James' Park means everything to me, it is a magical place. It is a special place for every single Newcastle United fan. Players come and go, managers come and go but Newcastle United and St James' Park stay the same."
Ashley's four-year spell in charge of Newcastle has rarely been quiet.
Since taking over in 2007 he has overseen a number of controversial managerial changes, most notably the sackings of Kevin Keegan and Chris Hughton and the appointment of Joe Kinnear, while the club were relegated from the Premier League in 2009.
He also tried and failed to sell the club as his relationship with the supporters, who dubbed him and managing director Derek Llambias the 'Cockney Mafia', reached an all-time low, while big-name players such as Joey Barton, Andy Carroll and Kevin Nolan have been allowed to leave.
The waters have been smoother of late, though, with the Magpies still unbeaten in the Premier League and enjoying a rare period of stability under Alan Pardew.
But Harmison believes this latest move, which was initially mooted in 2009 to much disgust, could undo recent progress.
"Of all the things Mike Ashley has done since he became owner, I think this is the one people will find hardest to forgive and forget," he added.
"It is a very sad day and it's such a shame because the team are doing well, Alan Pardew has done a wonderful job and everything was going in the right direction.
"I'm not anti-Ashley, I never have been. He, along with Derek Llambias, has got the club into excellent shape. Financially we're stronger than we have been for years, but this will explode in their faces."
Harmison admits fans will be forced to eat some of their words if the move proves to be a financial success, but hopes it is not just something that will benefit Ashley.
He said: "If it's going to mean we can compete with the big boys again financially then it will be a necessary evil. But we want to see concrete evidence the money is going to be used in the right way, not just vague assurances. If it stays as the Sports Direct Arena the only person benefiting is Ashley.
"Giving Pardew a war chest of £20-30million in January would be a start. This money has to be given to the manager, only then can I begrudgingly accept it makes sense. At the moment it feels like an insult."
Explaining the decision, Llambias said on Wednesday night: "Our aim for Newcastle United is to continue to deliver success for the fans and everyone associated with the club.
We must make this club financially self-sufficient in order to deliver that success.
"To grow sustainably and allow us to invest in our future, we will need to rely increasingly heavily on commercial income.
"These are very difficult economic times and the board have a responsibility to maximise all revenue streams for the benefit of the club.
"Stadium rebranding offers a lucrative way for clubs to secure significant additional income."
The Newcastle United Supporters Trust said fans had been "softening" their attitudes towards Ashley, but that the news had justified why people had remained "sceptical".
Writing on their website the Trust said: "The Newcastle United Supporters Trust conducted some research among Newcastle fans last month and there was recognition that the current board had done well in controlling costs and that they had conducted some good business in the transfer market.
"Allied to that, the team are sitting in the top three after the first 11 games and as a result, there was some softening of attitudes towards the owner.
"However, despite the goodwill that this has brought the owner, fans told us that they remain sceptical about his motivations.
"This latest news about renaming the stadium to the 'Sports Direct Arena' clearly demonstrates why they are sceptical.
"Newcastle's ground has been St James' Park for more than 100 years and two years ago Derek Llambias assured fans that the stadium's official name would always remain St James' Park as long as they were in charge.
"So, is it any wonder that fans told us they don't trust the board, want a new owner and why the majority of Newcastle fans want to own a stake in the club?"
Mark Jensen, editor of fanzine The Mag, insists Ashley and Llambias should have been building on the feelgood factor established by an 11-game unbeaten start to the Premier League season, which has left the Magpies sitting in third place in the table, rather than dropping the bombshell they did early this morning.
He said: "What the club has done just reinforces what everyone has thought about them, that no matter what strides the likes of Alan Pardew and the players might take on the pitch, there is always something from above that undermines everything.
"It's no coincidence that they have performed a typical politician's trick and waited until things are going well to slip in something like this on the back of a cut-price season ticket deal which has filled the empty seats. It's quite cynical.
"It showed when Keegan was here the first time as a manager that when you start a bandwagon rolling at Newcastle like he did, it's a pretty powerful force.
"They should have been spending these two weeks really reinforcing the feelgood factor."
Llambias has insisted selling the naming rights is essential if the club is to maximise its potential revenue streams in a tough financial climate.
However, Jensen is not convinced the proposal will do that.
He said: "Unfortunately, the writing is on the wall. The shirt deal is up at the end of the season and I don't think anybody would be surprised if we ended up with the ground as the Sports Direct Arena and Sports Direct as the shirt sponsor.
"As it stands today, this announcement has brought no extra money into the club, but they have seriously annoyed a large proportion of their fan base.
"Maybe now people who were thinking of buying a shirt or whatever from the club shop will think, 'Right, I'm not doing that'.
"Certainly in the short-term, the only person who is benefiting is Mike Ashley and Sports Direct.
"They are claiming this will help to attract a sponsor - I just don't buy that because with what's gone on in the past, Newcastle United and the Sports Direct brand is a mixture that does not send a positive message.
"Every club which has had its ground named after a sponsor tends to be a new ground, or in Manchester City's case, it's going to bring in massiveamounts of money.
"This seems to me to be all stick and no carrot."
Newcastle do not play at home again until Chelsea arrive on Tyneside on December 3, and while Jensen is expecting the fans to support Pardew and his players as fervently as ever, the mood is likely to be ugly.
He said: "People will continue to support the players on the pitch as they have always done no matter what the circumstances.
"But this will just reinforce the belief that Mike Ashley isn't running the club for all the right reasons.
"It's a very strange way to run a big business which happens to be a football club. I think there are much better ways of maximising the potential revenue than turning their fan-base against them."