Malcolm Turnbull has endorsed giving Liberal members a greater say in all of the party's activities as not only crucial for winning elections but a "moral" issue.
However, despite the prime minister's stance, 1500 members of the party are still expected to have what NSW Premier Gladys Berejiklian described as a "robust and at times heated debate" on Sunday.
Adding to the heat will be Tony Abbott's insistence on the special convention passing his so-called "Warringah motions", which would ensure sitting members can be challenged under the new system of grassroots member plebiscites to select candidates at a state and federal level.
Mr Abbott also wants members to have been signed up for two years before they can vote in plebiscites, in a bid to cut down on branch-stacking.
The prime minister told the convention while there were differences in the "detail" of the reforms, it was essential the party hand more power to grassroots members.
"The fundamental principle that I am so proud our party is committed to today is that every member should have a say," Mr Turnbull said.
"It is not just right politically but morally."
Mr Turnbull's moderate faction is working with members of the "soft right" on alternatives to Mr Abbott's motions - including a longer time frame for members to wait and the protection of sitting members from the new rules - but it was unclear who would prevail.
Mr Abbott told reporters he was encouraged by the prime minister's speech, which he believed represented "unequivocal support for one member one vote".
But he warned the convention needed to reject those who were promoting "fake democracy" and embrace the "true democracy" demonstrated in the Warringah motions.
"Reform is coming and it's obviously coming with the full support of the prime minister," he said.
"It's going to be good for the unity of our party and it's going to be good for the prospects of our party at the next election."
He said the Liberal Party remained the "principle representative of the conservative side of politics" in Australia and he didn't believe disgruntled members would leave if reform stalled.
"My very strong message to anyone who has been disappointed by our party is stay and fight."
He rejected suggestions the debate was about his leadership ambitions.
"This is a contest between factionalists who want to keep power and democrats who want to open up our party and I'm very pleased the prime minister and I are on the same side."
Liberal president Nick Greiner told the convention it would be "unfortunate" if the party steered away from it being a "broad church".
"I do notice ... some lack of that civility, some lack of that mutual respect," he said, taking aim at factional players.
"My plea to you ... is advocate with passion, but to not do it in a tradition of civility and respect is very unfortunate."
Liberal MP Alex Hawke, who is pushing an alternative to Mr Abbott's motion, said it was important only "genuine members" were involved in party processes.
"Nobody wants to see people ... try to get involved in parties they're not actually in favour of, and we don't want to see any of that."
The final result of the convention on Sunday will go to the state director and president who will prepare the party's modernisation plan to go before a future NSW state council meeting for endorsement later in the year.
NSW Liberals president Chris Downy promised the plan would be implemented "without fear or favour".
Ms Berejiklian said she wanted reform to go further and party members to robustly debate it.
"I know that this issue ... will be robust and at times heated, but that is a good thing, that is normal for a healthy thriving organisation."