At the same time, it has changed everything.
It has changed nothing in the short term despite the widespread assumption that the loss of a parliamentary seat will put the minority National Government more in hock to United Future's Peter Dunne and Act's David Seymour.
Mr Peters' triumph has changed everything longer term.
His game of divide-and-rule which has him pitting voters in regions that have suffered economic stagnation against their big-city cousins is the most serious challenge he has mounted to National's centre-right hegemony since he climbed aboard the anti-Asian immigration bandwagon some two decades ago.
With other parties now also arguing for curbs on the number of immigrants, Mr Peters has been casting around for an equally potent substitute for some time.
He has now found one.
To deal with National's minor party allies first, the notion they now have more leverage is more myth than reality.
The dynamics which govern the relationship between the dominant ruling party and its support partners is more than just a simple numbers game.
The reality is that the influence Messrs Dunne and Seymour have been able to wield over National since last September's general election is akin to that of an ant crawling up an elephant's backside.
The impact of a slight change in the balance of power is likewise negligible.
The evidence for saying that is that neither leader has gone to John Key to demand concessions and rewrite their confidence and supply agreements accordingly.
Both men are acutely conscious their survival as parliamentary entities is contingent on them adhering to an unspoken pact with National-leaning voters that neither politician destabilises the Government.
If they were to do so, those voters would turn on them, tossing them out of Parliament at the first opportunity.
It all makes Mr Dunne's opposition to now-dumped amendments to the Resource Management Act very much a one-off.
Neither he nor Mr Seymour can exercise such veto rights very often - and they know it.
On top of that, if a piece of legislation risks being knocked down, then National will not put it up.
It is also hard to envisage a third-term administration - especially one led by Mr Key - bringing contentious legislation before the House anyway.
If parts of National's legislative programme are too soft ideologically or unacceptably interventionist for Messrs Dunne or Seymour then odds-on Mr Key will get the necessary numbers from elsewhere.
Enter Mr Peters on Wednesday with an ''olive branch'' - his words - offering to do just that by being willing to negotiate with National over amendments to the Resource Management Act to help National get the broad thrust of its intended reform into law.
It was the New Zealand First leader's way of underlining how the by-election has changed everything.
The renewed relevance Mr Peters' huge victory has accorded his party prompted a series of positioning statements from the leaders of National and Labour.
The most significant was Andrew Little's declaration that as Leader of the Opposition, he felt obliged to ensure opposition parties operated in a cohesive fashion and presented a united front.
He acknowledged that did not mean Labour, New Zealand First and the Greens should not seek to maximise their vote.
But it did mean those parties should not trip over one another in attempting to defeat the common enemy - National.
Mr Little's call for unity is a complete departure from the pre-election stance adopted by his predecessor, David Cunliffe, who spurned an offer from the Greens to campaign co-operatively.
Mr Cunliffe later conceded that had been a mistake, saying that the ''progressive forces of politics'' would have done better if they had been better co-ordinated.
Mr Cunliffe may have been too hard on himself, however.
His rejection of the Greens' offer had much to do with the fact Mr Peters cannot abide the Greens and believes (correctly) that they are toxic to the kind of voter he is seeking to reach.
Given Labour and the Greens were never going to win enough seats combined to dethrone National, Mr Cunliffe judged it was better to get Mr Peters on board and leave the Greens, who had nowhere else to go, with no choice but to prop up a Labour-New Zealand First administration.
If Mr Little can find a solution to that continuing conundrum, he will be judged a politician of rare skill.
National believes Mr Little's call for opposition unity is far more self-serving than he is letting on, however.
National argues that weighing in behind Mr Peters' candidacy in Northland brought an abrupt end to Mr Little's growing momentum as Labour's leader and he has handed Mr Peters a huge advantage in the run-up to the 2017 election.
No-one seriously believes Mr Little can pin Mr Peters down and keep him under Labour's wing.
National thinks Mr Peters is on such a roll that he now believes he can supplant Labour as the second biggest party, at least in provincial and rural New Zealand.
Thus did Mr Key taunt Mr Little in Parliament by referring to him as the ''Junior Leader of the Opposition''.
National has little to be smug about, however. With his talk of ''two-tiered economies'' and ''second-class citizens'', Mr Peters is already looking well beyond Northland's boundaries to sell his message of government neglect to those in other regions, such as Gisborne, Hawkes Bay, eastern Bay of Plenty, Wanganui and the West Coast, who feel they too have been chucked on the economic scrapheap while metropolitan New Zealand prospers.
Mr Key's initial response to the Northland landslide was to position himself as having no truck with Mr Peters.
That only succeeded in prompting Mr Peters to try to force Mr Key to eat his words by offering to come to the party on the RMA.
Mr Key's dilemma is whether to risk being seen to kowtow to Mr Peters by accepting his offer to negotiate and thus look weak or ignore the offer and look arrogant and having failed to heed the lessons of the by-election defeat.
The prevailing feeling within National is that bitter experience suggests trying to negotiate with Mr Peters is a waste of time.
What will really be troubling Mr Key, however, is that Mr Peters' repositioning of New Zealand First as some kind of ''Country Party'' will see him wreaking havoc behind National's well-fortified front line.
That is Mr Key's nightmare.
The fall of Northland means there will also be sleepless nights for nervous National MPs who thought their seats in National's supposed ''heartland'' were safe forever.
• John Armstrong is The New Zealand Herald political correspondent.
