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Two-hundred-and-eighty-four competitors will now line up for the Longest Day and One Day Teams categories, starting in pods of fewer than 100.
Ninety athletes in the mountain run, who start from a completely different section of the course, will also get their opportunity to compete - with both events now going ahead on February 12.
Race director Glen Currie said it is still a significant decrease from the initial 1400 registered athletes.
Organisers were forced to cancel the two-day category earlier this week.
"There was simply no way we could provide a safe event for the two-day athletes, support crew and spectators. But, once more guidelines and information came to light earlier this week, we became confident that we could do so at a much smaller scale.
"Government feedback has been that they do not want events to cease altogether, rather they're asking events like ours to restructure to minimise contact of people as much as possible and reduce the potential of a mass spread as a result of the event," said Currie.
Athletes' support crews have been limited to just two people, while friends and family will be restricted from entering any of the athlete transition areas.
Food and beverage offerings would also be cut, impacting a number of community groups that often rely on the revenue as part of their annual fundraising, Currie said.
"We've traditionally been able to facilitate and donate up to $50,000 per event to the likes of the Springfield, Sheffield and Moana Schools, the Malvern Lions Club, Kumara Community Trust and a raft of others but unfortunately these changes to the event will have a knock-on effect."
The safety of athletes was one area that Currie said his team wouldn't be moved on.
They are continuing to work with Christchurch Helicopters, which provides heli support for the mountain run across Goat Pass, as well as the Canterbury Jet Boat Club, which patrols the 70-kilometre stretch of the Waimakariri River.
"This is one area that can't be compromised. But reducing the number of competitors on course should already see a reduction in the time that their services are needed across the day.
"Traditionally, the one-day athletes are the more experienced ones too, so their dependency on the safety crews is lower."
The Mountain run was originally scheduled to take place in conjunction with day one of the two-day event on February 11, however, in order for it to take place it has had to be shifted a day later.
"We know this will impact a few athletes with accommodation and travel arrangements, but with greater management comes greater cost and we need to find ways to accommodate as many people as possible," said Currie.
The first wave of competitors will start from Kumara Beach at 7am on February 12 and are expected to begin arriving into the finish area at New Brighton beach any time after 4.30pm.