The move to bring back the Monday element to the weekend celebrations which suffered poor ticket sales some blamed on a clash with Stirling Council's Armed Forces Day event was revealed in correspondence to MSPs.
Holyrood is examining what clan chiefs called the "sorry tale" of Bannockburn's 700th anniversary.
The Parliament's energy and tourism committee convener Murdo Fraser said yesterday concerns remained over the organisation of the event and officials from national tourism body VisitScotland would still be asked about when they first knew things were going wrong.
They will also be asked for assurances the latest version will break even.
Sir Malcolm MacGregor of MacGregor, of the Standing Council of Scottish Chiefs, said cutting the event had created problems for clan chiefs abroad as "most ticket sales would have been to the diaspora, as they tend to book early".
He added: "Homecoming 2014 has been dogged by uncertainty and controversy."
Around 35 clans with pitches are expected at what he said was the "ongoing debacle" of Bannockburn Live.
VisitScotland chairman Mike Cantlay said: "A proposal has been made to set aside Monday as an informal day for Clan Societies to gather.
"This proposal has been warmly welcomed by Council of Scottish Clans and Associations, Clan Chiefs and the Highland Clans Partnership."
The two days are also to be extended from 10am-5pm to 10am-7pm.
Clan chiefs and National Trust for Scotland (NTS) cited Stirling Council's late announcement that it was to stage National Armed Forces Day in Stirling over the same weekend after Bannockburn ticket sales reached just 2000.
Kate Mavor, NTS chief executive, said it threatened break-even targets.
Scaling back the main event to two days shaved £300,000 off the original £950,000 bill.
Stirling Council leader Johanna Boyd said as the organisation of the Bannockburn event was led by NTS and then VisitScotland, it could not comment on its ticket sales.
She added that a plan for guiding visitors and traffic over the weekend and joint marketing is proposed, involving organisers of both events.
Ticket sales for the two-day main event in June - with three re-enactments each day - have risen by 1500 since the country's tourism body took over promoting the event from NTS in January.
VisitScotland said the new figures for the event meant 26% in total had been booked, but this is out of an allocation of 20,000, more than half the original target of 45,000 ticket sales.
Mr Cantlay added: "Given that the formal marketing of Bannockburn Live has not yet begun, we view ticket sales to be encouraging at this early stage."
Mr Fraser said: "Despite receiving a written response from VisitScotland, the committee still has a number of concerns and we have agreed to invite the chairman of VisitScotland to appear in mid-March to provide further information and an update on ticket sales."
"We'll be asking VisitScotland for details of when they were first aware of the planned changes to the event and for assurances that it will at least break even and that no Scottish business will lose out if they become involved."
Details of the new third day are being planned with clan chiefs but will include access to the Bannockburn centre for clan members and possibly "activity from the Bannockburn Live event" as well as food and drink.