Supporters of democratisation in Labor’s left faction have gained two positive votes for rule changes that would give rank-and-file members a say in Senate preselections and in the selection of delegates for future party conferences.

Two of the four unaligned delegates at this year’s ALP national conference have signalled they will support Senate preselections and national conference delegates being decided through ballots in which rank-and-file members have 50% of the vote.

Support from the Victorian-based independents, Eric Dearricott and Sandra Willis, is a fillip for the cause of party reform at Labor’s national conference​ in Melbourne next weekend – but the outcome of this debate is by no means certain.

The national left at a meeting in early July formalised a negotiating position around democratising ​ the ballots, ​but the faction is not fully united behind the proposal.

The Senate preselection reform faces resistance from some trade union leaders. United Voice in Western Australia is currently opposed to the national left negotiating position, and there is also resistance in South Australia.

Changing the ​party’s rules at the national conference requires a statutory majority of 199 votes.

Given the tight factional balance at this year’s event, the left will need to bind all its conference delegates, and gain support from the non-aligned swing votes, to have any chance of success.

Even if those two things occur, some party sources suggest the 50% rank-and-file ballot proposal is unlikely to succeed.

New South Wales left delegate Darcy Byrne – a long time campaigner for Labor democratisation – has called on the left to get behind the proposal.

“With the right [faction] machine having lost control of their majority, left and independent delegates must work together at conference to deliver the democratic changes Labor’s future depends on,” Byrne told Guardian Australia.

“Given rank-and-file members now have half the voting power in electing the party leader, there is no reason Senate candidates and conference delegates shouldn’t have to face the music too.”

In a speech delivered last April, Labor leader Bill Shorten said future​ party conferences needed to be comprised of a “mix of people” and local Labor members needed to be given a “meaningful say in the selection of Senate candidates”.

The lack of specifics in Shorten’s position has given factional powerbrokers on both sides of the argument wriggle room to both advance and thwart the cause of party reform at the July conference.

Discussion is also continuing on ​ a push by the Labor Environment Action Network (Lean) to lock the parliamentary party in behind post-2020 emissions reduction targets consistent with recent advice from the Climate Change Authority, and behind a significant boost in renewable energy.

The ACT’s deputy chief minister, Simon Corbell, has called on the federal leadership to adopt the Lean position next weekend.

“This change to Labor platform would set two key goals, a 50% reduction in carbon emissions on a 2000 baseline year by 2030, and 50% renewables by the same year,” Corbell told a clean energy summit in Sydney on Wednesday.

“The resolution reflects the movements globally towards decarbonisation by 2050 and is consistent with the recommendations of the Climate Change Authority made earlier this year,” he said.

“If Labor is to have a credible progressive renewable energy agenda, it must start with this national conference resolution.”