City Republicans have won state Board of Elections approval for a new “Stop de Blasio’’ line on the November ballot that will allow voters unhappy with Mayor Bill de Blasio — and perhaps Donald Trump as well — to back their two Assembly candidates without having to vote the GOP party line.

New York County GOP Chairwoman Adele Malpass told The Post that the purpose of the new line, approved on Friday, was to give the large numbers of Democratic and independent voters who polls show are unhappy with de Blasio’s policies a place to cast their ballots without feeling uncomfortable about voting Republican.

Malpass also said that if, as expected, the “Stop de Blasio’’ line draws a large number of voters, its use will be extended citywide next year to back the Republican Party’s candidate for mayor — assuming de Blasio is running for re-election.

“We’re hoping this becomes a movement into next year,’’ she said.

Malpass said she was surprised at the ease with which petition carriers were able to obtain well beyond the 1,300 signatures required to create the “Stop de Blasio’’ line in each of the Assembly districts, noting, “We’d go out on the street for signatures saying that we’re creating a line to stop Bill de Blasio and lots of people would say, ‘I’m a lifelong Democrat but he’s got to go.’

“We had people saying, ‘We’ll sign anything to get rid of de Blasio,’” she said.

The two Republicans who will be running on both the GOP and the new party lines against incumbent Democratic Assembly members are Rebecca Harary, challenging Dan Quart in the affluent Silk Stocking District on the East Side, and Jon Kostakopoulos, challenging Rebecca Seawright, whose East Side district is just to the north of Quart’s.

Malpass denied that the new line was created to give Republicans and others opposed to Trump a place to vote other than the GOP line, saying the focus was “strictly de Blasio.”

But a prominent Republican activist told The Post, “There are a lot of Republicans, not to mention Democrats and independents, who won’t vote for someone on the same line as Trump, so this is a smart move to give them an alternative.’’

Speculation that state Comptroller Tom DiNapoli will challenge Gov. Andrew Cuomo in the Democratic primary for governor in 2018 increased after de Blasio recently came to DiNapoli’s defense in the wake of Cuomo’s verbal attack on the well-liked official.

“Obviously, the state comptroller should be respected,’’ de Blasio said, referring to what many Democrats saw as Cuomo’s demeaning attacks on ­DiNapoli after several of the comptroller’s audits questioning the effectiveness of the governor’s already controversial economic development projects.

State Democratic insiders said de Blasio, if he survives an expected Cuomo-inspired primary challenge next year, would be ­DiNapoli’s most powerful ally in taking on the governor in 2018.

Meanwhile, speculation that DiNapoli is contemplating challenging Cuomo will likely be increased by spokeswoman Jennifer Freeman’s repeated refusal — when pressed by The Post — to unequivocally rule out a challenge.